Who's Your Partner in Success? Mercedes-Benz's f!) PartsPro
You've chosen your career as an ISP
(Independent Serv ice Prov ider) because you enjoy mainta ining, diagnosing, and repa iring
motor vehicles. One of the most challenging
pieces of your business is parts procurement.
Find ing the right parts at the right price and
being certain they w ill arri ve when promised
can be a challenge.
Wouldn't it be nice if there were a way to
get the par ts you need w ithout the hassle
and uncer ta inty, so you can get back to the
important business of actually fi x ing cars and
tak ing care of your customers?
With the Mercedes-Benz PartsPro wholesale certi Fi cation prog ram, now there is!
Pa rtsPro is a rigorous program intended
to t rain Mercedes-Benz dealership pa rts
departments on how to better take care
of you and ultimately your customers.
Par tsPro certified dea lers have elevated their commitment to supporting the independent repair channel, and w i ll prov ide you wi th the
highest level of customer ser v ice. They focus
on the things that matter most to you!
CONVENIENCE ... AccuRACY ... PROFITABILITY . . . DELIVERY
A PartsPro dealer has the tools in place to better meet the needs of their es teemed wholesale customers.
For a dea lership to achieve Par tsPro
Certificat ion, parts department person nel must
first undergo intensive "customer-cent ric"
2 Mercedes-Benz StarTuned
t raining which teaches person nel how to better help YOU.
There's far more to PartsPro than just
customer-serv ice tra ini ng. The dealership must
make specific comm itments to provide "Best in
Class" ser v ice in areas such as logistics, which
includes ISP-focused parts ava i labil ity, regular
deliver y serv ice, outs ide sa les people to prov ide you personal ized serv ice, as we l l as a dedicated
phone line and "w ill ca ll " pick up area.
THEN THERE'S TECHNICAL HELP. On occasion we all need a helping hand. Your
Pa rtsPro dealer is there to assist. Whether it mea ns prov iding, diagnostic ass ista nce, information on suppl ies or special too ls, or
anything else you may need to assist you in repa iring your customers' Mercedes-Benz
vehicles and get them back on the road as fast
as poss ible.
Only those dealerships that meet the stringent cert ification requ irements earn the r ight to
display the "PartsPro" logo. Additionall y, t hey
receive ongoing consul tation and tra in ing to
ensure that they are consistently provid ing the
very best suppor t to you, the ISP customer.
We hope you are already receiv ing indust ry lead ing serv ice from your Mercedes-Benz dealer; however, once PartsPro Cert i fied, we believe you' ll be thri lled w ith the new "Best in
Class" parts-procu rement experience!
Of course, you'll cont inue to have the
peace of mind that i nstalling only Genuine Mercedes-Benz par ts can prov ide. I
..
TO OUR READERS:
Welcome to STARTUNED, the magazine for independent service technicians working on Mercedes-Benz vehicles. Your MercedesBenz dealer sponsors STARTUNED and provides the information coming your way in eaoh issue. Mercedes-Benz wants to present the information you need to know to diagnose and repair Mercedes-Benz vehicles accurately, quickly and the first time; text, graphics, on-line and other technical sources combine to make this possible. Feature articles, derived from approved company sources, focus on being useful and interesting. Our digest of technical information can help you solve unanticipated problems quickly and expertly. We want STARTUNED to be both helpful and informative, so please let us know just what kinds of features and other diagnostic services you'd like to see in it. We'll continue to bring you selected service bulletins from Mercedes-Benz and articles covering the different systems on these vehicles.
Send your suggestions, questions or comments to us at: STARTUNED One Mercedes Drive Montvale, New Jersey 07645 Phone: 1 201.263.7284 E-mail: [email protected]
STARTUNED is a publication of Mercedes-Benz USA, LLC ("MBUSA"). No part of this magazine may be reproduced without the express written permission of MBUSA. Editorial and Circulation Offices: 1348 River Road, Montague, NJ 07827. CAUTION: Vehicle servicing performed by untrained persons could result in serious injury to those persons or others. Information contained in this magazine is Intended for use by trained, professional auto repair technicians ONLY. This information is provided to inform these technicians of conditions which may occur in some vehicles or to provide information which could assist them in proper servicing of these vehicles. Property trained technicians have the equipment, tools, safety instru:tions, and know-how to perform repairs correctly and safety. If a condition is described, DO NOT assume that a topic covered in these pages automatically applies to your vehicle or that your vehicle has that condition. STARTUNED is a registered trademart of MBUSA.
Group Publisher Christopher M. Ayers, Jr. [email protected]
Contributing Editors Bob Chabot [email protected]
Kerry Jonnson [email protected]
Michael Klaas [email protected]
Tom Nash [email protected]
Frank Walker [email protected]
Editorial Director Bob Freudenberger [email protected]
Technical Advisor Tim Amun
MBUSA Technical Content Advisor Donald Rotolo [email protected]
MBUSA Project Manager Stefanie Schweigler [email protected]
Art Director & Circulation Mgr. Christopher M. Ayers Ill [email protected]
Visit us at our web site www.MBWholesaleParts.com to view this issue and past
issues of StarTuned, along with a wealth of information on Genuine Mercedes-Benz Parts.
To locate a Mercedes-Benz dealer near you, go to www.mbusa.com.
IN THIS Issue
4 WHY You SHOULD Use ONLY GENUINE MERCEDES-BENZ PARTS
There's a lot more substance to this topic than you might think - it's not just marketing hype. The rigorous "Genuine Parts" testing program is especially interesting and relevant to the price/ value relationship.
12 MODERN MOTOR MOUNTS
Mercedes-Benz has always been an innovator in the automotive industry, and its powertrain technology shows this clearly. But besides the great leaps in engines that have produced the wonderful performance and efficiency of today, has anybody ever given any thought to how those engines are mounted in the chassis? Yes, indeed, and to a larger extent than you probably suspect.
20 MOST DEFINITELY, FROM D2B
The addition of electronics has turned the average vehicle into a technological marvel, but a Mercedes-Benz is no average vehicle. At the cutting edge of technology since its founding, the company has added fiber optics that allow it to process large amounts of digital media. What do we need to know if it stops doing that?
28 BUMPER TECH
The safety sensors are embedded in or attached to the bumper and front grille, which makes bumper repair after a collision very different from the procedures of only a decade ago.
Why You Should Use Only Genuine Mercedes-Benz Parts
There's a lot more substance to this topic than you might think - it's not just marketing hype. The rigorous "Genuine Parts" testing program is especially interesting and relevant to the price/value relationship.
4 Mercedes-Benz StarTuned
Fuel pumps need to be j ust right, or there 's potential for noise.
I n the last issue of StarTuned, we talked about why you should use only genuine
Mercedes-Benz brake parts from your loca l dealer in your service work, and we bel ieve the reasons we gave were pretty compelling.
We found the subject so interesting and important that we decided to do an addit ional article to explore the parts situation in
Mark Boege, a New Jersey ISP, tells StarTuned that he's always satisfied with Genuine Mercedes-Benz parts.
general, and the rationale behind you, the ISP (Independent Service Provider), stay ing w ith genuine M-B O.E. components. Much of this has to do with the company's commendable U.S. parts-testing programs.
In the previous article, we mentioned how genuine Mercedes-Benz brake parts were the best th ings to use because they were engineered and tailored for the characteristics
of the speci fie model invo lved, not just generica l ly one-size-fits-all. It turns out that that's the case with most of the parts you buy from your loca l M-B dealer.
OBVIOUSLY, SEEING THE ROAD CLEARLY IS IMPORTANT TO SAFETY
Take windsh ield w ipers, for example. With Genuine M-B parts, their cu rve matches that of the w indscreen of each model, so the pressure on the blade/glass interface is opt imi zed. Whi le compet ing w iper blades are made of poured rubber, Genuine M-B blades are extruded, which g ives better performance and a 20% lower wear rate -- they' re tested for 1.5M cycles! They also have a helpful wear indicator that changes
When sourced from Mercedes-Benz, big assemblies, such as this 7G-TRONIC transmission ...
June 2014 5
.. or this remanufactured engine have the industry's strictest quality control, and carry unequalled warranties. They're also often the subject of aggressive price-cutting programs.
color when replacement is needed, which
amounts to a g reat sales too l. Instal lation is far easier and faster, too, without all the confusion
of the various attachment parts of aftermarket
versions. If you look at it over the course of
a year, thi s can add up to hundreds of dollars
worth of labor.
Or, how about fi lters? With cabin air filters, the time required for installation also adds up. Genuine Mercedes-Benz cabin filters can
be installed more quick ly because they don't
have to be modi fied to make them fit. Seal ing is optim ized, as well. The seal is tested for blow-by w ith special equipment that measures particles in the air.
Air filters are tested for 2,000 miles over the
same route. The tests have proved that the use
6 Mercedes-Benz StarTuned
The cost of replacement engine management computers (PCMs for Powertrain Control Modules, to use SAE's standardized terminology) is another thing on which Mercedes-Benz has instituted money-saving programs.
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·-The EPC (Electronic Parts Catalog) is sophisticated and comprehensive. You'll always get the right part the first time. It's free, too. Just visit http:/l__epc.startekinfo.com.
of genuine air fi lters has a substantial impact
on fuel efficiency. Especial ly w ith diesels,
performance also goes down when a nongenuine part is installed.
INDEPENDENT TESTING IN THE U.S.A. We've mentioned tes t ing, but the Mercedes
Benz Genuine Parts Testing Program is much
more comprehensive and appropr iate to ou r
market than you probabl y know. The test ing
is designed to measure the actual impact the quality of the par t has on the customer. In other word s, for rea l-world situat ions, not for
some ivor y-tower idea.
Tes ting is done in the U.S., which assures
that the findings are rea lly market-appropr iate.
Not only does Mercedes-Benz se l l more vehicles in this country than anywhere else, the U.S. also has special conditions (there's
nothing in Europe equal to Death Val ley),
differen t fuel blends, bigger
engines, and un ique regulations.
Th is is true road testing; it 's not done on a dynamometer.
The locat ion with in the U.S. is chosen according to the type of
part being tested. For example,
testi ng brake pads in the bruta l
stop-and-go traffic of Los Angeles
is idea l. Both genu ine O.E. and aftermarket l inings are installed
on vehicles that a re cl r iven on a predefined route for one month.
The driver has a "cl icker," which
he or she can hit during a brak ing
event that exhibits issues such
If you've been in the auto service business for any leng th of time, you 've seen problems with the quality of aftermarket remanufactured alternators. This is never an issue with Genuine Mercedes-Benz parts.
as noise or vibration so that the on-board equipment records it . Microphones are used for brake noise, and brake dust is measured with a photometer. Even something
as subjective as pedal feel is eva luated. Once again, testing is
for impact on the customer.
June 2014 7
Who conducts a\\ this disciplined testing?
In ever y case, Mercedes-Benz employs
independent laboratories to be sure the resu Its
are from an objective third party and are not
skewed by brand loya lt y.
CONVENIENCE, SPEED, AND ACCURACY MBUSA offers a powerfu l tool that can
streamline your parts-sourci ng research
efforts: The EPC (Electronic Parts Catalog),
a comprehensive and easy-to-use parts look-
up system. It's a big help and t ime-saver in
searching for exactly the right part, assu ring
that you'll always get the correct thing the
first time (which is often not the case in the
aftermarket). This w ill go a long way toward
avoiding the schedu l ing disasters that can make
customers unhappy with you. The download
is free -- visit http:/Jepc.startel<i nfo.com. We
believe you' ll actually enjoy using it.
Something that's not often mentioned is the
problem you may have finding a specific part
for an older model -- Mercedes-Benz owners
typica lly keep their vehicles for a long, long
time, so it's likely that you' ll often have cars
in you bays that almost qual i fy as vintage, or
even classic. You can waste a lot of time and
end up frustrated searching for parts for these
venerable vehicles from the aftermarket, whereas
the EPC covers them in detai l, and inventories are scrupulously maintained even for what are
sometimes ca lled "heri tage automobiles" (they
may very well be used as daily drivers).
There's more to electronic parts sourcing aids.
MBUSA has launched the new www.mbwholesa leparts.com. Among its useful
features are model designation charts and
technical information resources that will help you
order the right parts and make installations easier.
Those electron ic aids combined w ith the
superior quality, competitive pricing, and
excellent warranty protection you get when you make the commendable dec ision to purchase
8 Mercedes-Benz StarTuned
genu ine Mercedes-Benz parts wi ll contribute to your peace of mind and reputation.
PRICE/VALUE Over the years, we've seen various carmakers
overcharge for their O.E. parts to an egregious extent,
trusting that obedient motorists or shop owners
wou ldn't question the amount. One example that we
especially remember was a sensor for one upscale
make that the dealers charged over five times more
for than the same Robert Bosch part number could
be bought elsewhere.
That's not the kind of high-handed pricing
pol icy Mercedes-Benz fol lows. The company
does a yearly evaluat ion to make sure its
Genuine Mercedes-Benz replacement batteries are made by the best European manufacturers.
Basic aftermarket catalytic converters that barely meet EPA guidelines are notorious for having short lives. This genuine replacement unit will last as long as the original.
¥:co\tr Workshop Resource to Get the Job Done • WIS-net (Workshop Information • Maintenance Sheets
System}
• Wiring Diagrams
• Technical Bulletins
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• Star Diagnosis System (SDS)
• Mercedes-Benz Workshop Equipment
@ Mercedes-Benz
prices are competitive. lt's often found that certain parts, fue l filters for instance, are
more expensive from aftermarket suppliers.
And there's never an issue w ith quality, fit, or
warrant y protection when you go genuine.
® Mercedes-Benz
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I t can be difficult to find parts for an older model, such as this Klima relay, from aftermarket sources. Searching for them takes your valuable time when you could simply go genuine and have easy sourcing from Mercedes-Benz.
10 Mercedes-Benz StarTuned
As Kerry Jonnson, one of our es teemed
technica l contri butors to StarTuned, has
stated, "In the automotive repa ir business, our
customers rely on us to prov ide the type of
serv ice that allows them worry-free operation
of their vehicles. They don't understand how
complex these vehicles have become. They
just know they need their vehicles to operate in a safe and pred ictable manner. Here is
one buy ing decision you can make that will
help you achieve thi s goa l." That mea ns
"partnering" w ith your local Mercedes-Benz
dealer 's pa rts depar tment.
We' ll conclude w ith a statement from another Mercedes-Benz expert: "Say you have a customer
who's spent lots of money to buy a nice E-Class.
Using non-genuine parts wou ld be li ke replacing
a link in a chain w ith a paper clip. It impacts the
entire performance leve l of the car." I
It's not only parts, but also tools and equipment. Where else can you get something like this comprehensive electrical connection kit but from your local Mercedes-Benz dealer?
It seems to be in the genes
of Mercedes-Benz engineers
to cont i nuously look for any
possible way to improve the
company's veh icles. Every aspect
of those vehicles is thoroughly
evaluated and an incredible
amount of thought goes into
every component, both ex isting
and yet to come. Even something
as simple as a door handle is
studied and improvements are
made. Most people don't g ive
much thought to door handles, but
Mercedes-Benz has engineered a
stronger one so that i n the event
of an accident you can get a good
grip and open the door even if
it has been damaged. This may
seem like a small improvement,
but we're sure first responders
appreciate th is simple feature.
This is how Mercedes-Benz
approaches everything that its
vehicles are composed of. Over
the years, all ki nds of dramatic
technologica l advancements
have been introduced into
the automotive i ndustry, and
Mercedes-Benz has typica lly been
a leader in th is.
Tn recent decades, the world of
personal transportation has gone
through such rapid evolut ion
that perhaps "revolution" is a
more accurate word. As high
technology has taken over, serv ice technicians have seen
more clearly than ever before
the need to keep pace w ith it.
Modern electronics started with
fuel inject ion, ign ition, and
feedback engine management
sys tems to control emissions
and increase fuel economy. The
electronics revolution con tinued
with ant i-lock brake systems
(ABS), then t raction control and
the Electronic Stability Program
(ESP). Mercedes-Benz was one of
the fi rst manufac turers that, in
conjunction w ith Robert Bosch
A.G., developed CAN (Controller
Area Networks). Th is led the
way for indiv idual computerized
systems to become integrated
and work with each other to
form systems like ESP. A ll th is
computer ization, of course, adds
a certai n level of complex ity to
our jobs w hen something goes
wrong. It's our responsibi lity as
technicians to lea rn continuously
so we can prov ide competent
diagnosis and ser v ice to our
customers. There are some
components, however, that you
probably never wou Id associate
w ith electronic controls -- motor
mounts, fo r exa mple.
PROACTIVE There is a debate in th is country
over whether the automotive
i ndustr y has suffered more
from government bu reaucracy
forc ing unnecessary change, or
from the market forcing more
socia lly-responsible developments.
Regard less, Mercedes-Benz
has responded admirably to
these challenges. One of its major initiati ves has been the
development of diesel engines that
g ive luxury vehicles levels of fuel
efficiency prev iously achieved
only by sub-compacts, along with
astonishing performance and low
em iss ions. Those attributes still
wouldn' t sway the American consumer, however, if NVH (Noise, Vibration, Harshness) hadn't
been reduced al most to the levels of a gasoline
burners. One of the factors in the success of that
effort was the invention of an entirely new type
of motor mount.
Through most of automotive history, motor
mounts have been mundane. In early cars, they were simpl y brackets, bolts, and nuts
that held the engine rigidly to the chass is. Of course, that meant that all the v ibrations,
jerks, and shocks that originated w ith i nternal
combustion were transferred directl y to
the unfortunate dri ver and passengers. It wasn't long before mit igating that motoring
unpleasantness became a priority. The first, and longest-running, attempt at accomplish ing
this reduct ion in v ibration was the adoption
of mounts that incorporated rubber isolators
to absorb part of the unwanted harshness any
rec iprocating assembly transmits. Sta rting in the
earl y 1930s, thi s idea was
reasonably successfu l, if not ideal.
Much more could be
done to isolate the delicate
occupants of a vehicle
from internal combust ion's basic brutality. So, Mercedes-Benz eng ineers
developed motor mounts
that did just that.
Most of the company's vehicles currently on the road have hyd rau I ic
engine mounts that
Engine mount design: 1. Flange 7. Hub 2. Seal bellows 8. Retaining ring 3. Diaphragm 9. Cover 4. Check ball 10. Bore 5. Buffer stop 11. Solenoid 6. Protective cap
go beyond the simple idea of using rubber's
compressibili ty to reduce
roughness -- oi I is the medium used to dampen the v ibration a running
The two-wire harness is a surefire give-away that this is a computercontrolled mount. It is powered up by fuse F58. If you unplug the fuse and plug it back in with the key on, you should hear the mounts click.
14 Mercedes-Benz StarTuned
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With a paid subscription to www.startekinfo.com you can access wiring diagrams. Here, you can see that components Y123 and Y123/1 are the switchable engine mounts. They're wired together so both mounts get grounded at the same time by the ME.
Ml (Fuel pump)
M4n (Combustion engine and air conditioning with Integrated control
fan motor) M16/6 (Throttle valve actuator)
M55 (Intake port shutoff actuator
a motor) Ulll R39/1 (Vent line heating e lement)
• R4B (Coolant thermostat heating
l!!!I element •!- -II Y77/1 (Boost pressure postt loner)
YB5 (Exhaust gas recirculation cooler bypass SWltchover valve) Y2719 (Exhaust gas recirculation actuator) Diagnostic glowing
Injector shuto!T
Status of associated actual value
Name Actual value Spacllledl4•• Switchable engine mounts Fault. 53336/6058
I:> Actuate components ·y123 (Len switchable engine mount)' and 'Y123/1 (Right switchable engine
mount)'.
Terminate actuation.
If you have made the investment in Xentry, you have the ability to bi-directionally control outputs. One of these is the switchable engine mounts.
June 2014 15
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engine generates. Somewhat similar
to the pri nciple 0 ... . - . ~ c:> o:o: t ... - ·] a lil f-·,;..,:J c.:i - · - · ,.,. ,. , -~ •O.-~1°"**"....,.Jr.,._....,..
... ENGINE 642 In MODEL 166 of a suspension
shock absorber, the oi I is forced th rough an ori fice
between two
chambers at the top and bottom of
the mount as they
are compressed and expanded
; 11~R!ii!iliim!!i=iliiiil ...
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by engine shake.
When these fa i l,
it's from a loss
of fluid, and
typica lly causes
a more sudden
These modern motor mounts are still serviced in the same way as a conventional unit with the minor exception that there is an electrical connector to unplug. With your paid subscription to www.startekinfo.com, you can access WIS and get a step-by-step procedure for diagnosing and replacing the new mounts.
and pronounced clunking than you'd get from a graduallydissolv ing rubber mount. Diagnosis is mostl y
a matter of observation. l s the bottom chamber fl at? Is there oi l present?
Speaking of the work ing fluid, whenever
you're try ing to track down an oil leak, say
from a cam or t iming chain cover, don't overl ook the possibility that the rea l culprit is a ruptured motor mount. We should also ment ion
that some aftermarket parts suppliers subst itute
ordinary rubber mounts for the hydrau l ic type,
wh ich is another reason you should stick w ith
Genuine Mercedes-Benz parts.
COMPUTER CONTROL? While hydraulic motor mounts work qu ite
well, they're still passive. They have no ability
to adapt to the differi ng cond itions encountered
as engine modes change. Since transforming
the public perception of the characteristics of diesel-powered cars is turning out to be a lengthy process, Mercedes-Benz has been doing everyth ing possible to reach that goal. Not
only with sophisticated common-rai l injection
16 Mercedes-Benz StarTuned
with multiple events and ingenious aftertreatment of the ex haust, but also by givi ng an unsung and overlooked part a fresh look:
the lowly motor mount. In order to endow its
diesels w ith a smoothness that r iva ls that of a
gasoline eng ine, Mercedes-Benz has developed computer-controlled mou nts.
These new "e lectri c" or "switchable" engine mounts were introduced in 2011 on the
Mercedes-Benz M-Class w ith the 642 diesel
(166 Chassis). Instead of hyd raulic oil , they
use air conta ined in three bel lows. An internal
electri ca l solenoid valve either connects the air chambers together, offering a large vo lume of air for the compression and ex pansion that
absorbs v ibrations, or closes off the chambers from one another for a firmer mounting (the default position is the "hard" setti ng w ith the
chambers isolated).
Two w i res run from the harness to the solenoid, one 12V, and the other ground, which is controlled by the ME (Motor Elec tronics). Even with sophisticated common-rai l injec tion, diesels can be rough during cran king and
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Here we are looking at the activation of the switchable engine mounts with the Xentry software. Notice how the ME simply grounds the solenoids in the upper trace. The lower trace shows the amperage draw of a single engine mount.
start ing, and tend to shudder when shut down. So, the ME is programmed to activate
the solenoid during these modes, making a relatively-large volume of air avai lable to absorb any harshness. This is ca lled the "soft" sett ing.
The solenoid is either energi zed or off, there's
no in-between.
XENTRY AND DMM Although you may not be seei ng these mounts
for years, you shou Id sti 11 know how to diagnose them. I f you've invested in Xentry software, you
can ac t ivate the solenoid at w i l l and monitor both the amp draw and the computer's ability
to control the ground side of the circu it. You
can also use your DMM (Digital Multi-Meter)
to check the resistance of the solenoid and look for an open windi ng. You should read about 27
ohms with a good solenoid.
The power feed is fu se F58. This fuse also
supplies the diesel fuel injection system solenoids, the pressure regulating va lve, and
the quantity control va lve. So, a short circuit
or any other fai lure that causes the fu se to blow wi ll cause a no-start cond ition, and the mounts
wi ll default to "hard," which won't be noticed
with the engine stopped. These mounts may be
incorporated into other models in the future, so be sure to check the w iring diagra ms for the car at hand by v isiting StarTek lnfo.com.
Remova l and replacement is basica l ly the
same as with any other engine mount. There
are two fasteners that hold it to the engine sub-frame, and a sing le fastener to the engine mounting bracket. The only add itional step is
unplugging the elect rica l connector.
As we sa id earl ier, with modern technology
being appl ied to more and more aspects of automobiles, it is your responsibil ity as an
ISP (Independent Ser vice Provider) to keep pace with these changes and continue your education. This allows you to keep giving your
customers what they expect from you. It 's also in your own best financial interests. I
Ju ne 2014 17
er ormance.
uccess. With our competitively priced Genuine Remanufactured Parts, you no longer have to settle for anything less than Mercedes-Benz quality. But that's just part of the story. You see, our airmatic struts, catalytic convertors, turbochargers and steering racks all carry a 1 2-month, no mileage-restriction warranty. So our parts are not only a great deal. They're a great value. And since they're genuine Mercedes-Benz, you can have confidence they'll last, and so will your relationship with your customers.
Contact an authorized Mercedes-Benz dealer or learn more at www.mbwholesaleparts.com
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A 163 '490 971'4 80
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• MSRP excludes state and local taxes and freight if applicable. Price excludes core deposit. Price valid as of February 2014. Prices may vary by dealer. See your authorized Mercedcs·Benz dealer for additional details or a copy of the Mercedes-Benz parts limited warranty .
MOST Definitely, from D2B The addition of electronics has turned the average vehicle into a technological marvel, but a Mercedes-Benz is no average vehicle. At the cutting edge of technology since its founding, the company has added fiber optics that allow it to process large amounts of digital media. What do we need to know if it stops doing that?
One of the first steps in diagnosing a problem with the MOST bus system is to establish communication with the MOST master control unit. In this case, it is the COMA ND ® radio. Verify communication first. If you do not have communications, check the fuses, power, and ground to the control unit. If you have communication, you can move on to the next step.
20 Mercedes-Benz StarTuned
We've all seen electron ics take hold of ou r
industry. It started with electronic ign ition
(mandated in 1975), then fuel injection, and now
seemingly every component on the car is either
contro lled or monitored by electronics. This
generall y makes systems more complicated. There
are sensor inputs, a processor, and computer
controlled outputs. While this added complexity
can make your life more difficult when something
breaks, it can also make it easier.
SDS XENTRY software is designed to interpret
the data of the processors and can retrieve
diagnostic trouble codes, g ive you rea l-time data,
and also allow you to bi-directionally control
computer outputs so you can find out if the
components receiving commands are actually
working. Having this in formation allows you
to quickly look at data you may find useful in
diagnosing the problem. Once you isolate where
the trouble is, you can then do more specific
electrical test ing to verify your conclusions.
You'd feel pretty si lly if you spent hours doing
high-tech diagnosis on ly to find out that an
electrica l connector was not plugged in properl y.
GETTING THE MOST Nowhere is thi s technology more evident
than in the entertainment system. These have
different needs from body control or powertra in
systems. Powertrain systems need high-speed
data transfer because t rac tion control , engine
management, and suspension features need
to work together to keep the car under control
during spirited drivi ng. Body control systems
ca n operate at a much slower speed and the
vehicle's occupants won't notice the difference.
Entertainment systems do not need high speed,
but there is a whole lot of in formation that needs
to be moved around --visual and audio media
files are large. This in format ion must be sent
from the d igital med ia reader (CD/ DVD player),
the display screen, and the sound system. If
these systems transferred information across
electrica l lines the w iring involved would have
to be ver y complex. For thi s and other reasons,
Mercedes-Benz has chosen to use fiber optics for
transferring digital media.
Fiber-optic systems offer many advantages
over conventional elect rica l wiring. Number
With a paid subscription to www.startekinfo.com, you can pull up a chassis-specific wiring diagram. You can compare the wiring to the MOST bus list of control modules and locate each component. Notice that the Orange lines are wired in series. This is the fiber-optic line. The purple wire is the electrical "Star" wiring electrical bus the MOST master uses to see which control units are waking up and which are not.
one, they are capable of carry ing large amounts of data very qu ick ly. Number two, fiber-opti c
systems send I ight messages along a cable, so
they're not subject to magnetic inter ference, or
RF!. They do requ ire a discrete fiber-optic l ine
routed with the w iring harness, which does acid a level of complex ity. Fiber-optic cable is fa irly
sturdy, however, and is not subject to corrosion from water intrusion as elec trical wiring is.
The main ru le for routing fiber-opti c cable is simply not to bend it enough to crimp it.
Usuall y, you don't have to worry about the cable un less accident damage has compromised it. I n
that event, replace it.
MASTER Mercedes-Benz started its adopt ion of fiber
opti cs with the D2B (Domest ic Digital Bus)
system, which was developed exclusive ly by the company. The net work is routed in seri es -- there
is one fiber-optic cable coming in and another coming out. In order fo r this system to work,
"someone" has to be in charge, so every D2B
system has a "master." This is the one control
unit that is in charge of all the others. Th is is
important to know because th is is the con trol
unit you are talking to when you communicate
w ith it using the XENTRY diagnosti c software. Since the fiber-optic network is routed in ser ies, it is important for the codi ng of the
master control un it to not only k now al l of the
components on the fiber-optic r ing, but also the
order in which they are connected. Not every
D2 B system is the same --someone may have ordered a car w ith or w ithout a mu ltiple-disc CD changer, for example.
Another thi ng that's important to know about
a series-wound fi ber-optic system is that i f one
component fa i ls it can bring down the whole
system. Nothing w i ll work. You may th ink it would be a big undertaking to diagnose a whole system that is not working, but it is rea l ly not that di fficu It. The Fi rs t th ing you need to
es tablish is communicat ion with the master
22 Mercedes-Benz StarTuned
Locate the first component on the fiber-optic bus and unplug the connection to that unit . When you turn on the ignition key, you should see one of the cables light up with the fiber-optic signal as shown here. Plug i t back in and move on to the next control unit until y ou no longer see the cable light up. This means either the cable is bad, or the control unit before it is not putting out a fiberoptic signal.
control unit. In the case of the D2B system,
the master is the COMAND® control unit -- the
interface mounted in the center of the dash. Use
your XENTRY software, or eq uiva lent, to try to
establish communication w ith the master. I f you do have communication, then you can assess
li ve data about the other control units on the
028, pu 11 diagnost ic troub le codes that may lead
you to the problem, or "p ing" the control units
on the D2B bus and see what answers back.
STARTING POINT If you do not have commun ication w ith the
master COMAND® un it, that's the first thing
you must fi x. Start with check ing power,
ground, and the wake-up signal to the control
unit. Remember, if the master is not functioning
then nothing else wi ll , ei ther. The first thing
you should check are the fu ses that power up the master COMAND® unit. I f the fu ses
have power, the nex t step would be to pu l l the COMAND® unit out and veri fy the power and
ground supply to it -- check for damaged or corroded w iring. lf you have power and ground,
then you may want to put a lab scope on the CA lines to the COMAND® unit and ver ify
that the scan tool communicat ion signal is
making it to the module. I f every thing is there, then you may simply have a bad COMAND®
unit. Mercedes-Benz offers remanu fac tu red
uni ts through you r Mercedes-Benz dea ler's pa rts depar tment.
I f you have commun ication with the
COMA ND® unit, t hen the diagnosis is even
easier. If the system is down, it has probably set a diagnostic trouble code in the COMAND®
unit. This wi l l probably lead you to the trouble, but even if it doesn't there is testing you can
per form to isolate the problem. From the master
COMAND® un it, you ca n cal l up the cod ing for
the unit and you w i l l k now what opt ions are installed in the vehic le you are work ing on.
This is a big help in diagnosi ng the fiber-optic system. What you ca n do at thi s poin t is access
the first contro l uni t the fi ber-opt ic signal is sent to and unplug the cable from that cont rol un it. Turn the ign ition l<ey on and obser ve the
If you purchase a fiber-optic loop, you can bypass a possibly bad control unit. If the system starts to work, you'll know the control unit is the problem. Before replacing the control unit, verify that it has the proper power supply feed, ground, and wake-up signal.
June 2014 23
cable plug. You should see one of the cables blinking. This is the optica l wake-up signal
from the master.
THE NEXT STEP
If you see the blinking light, you know the master is putting out the optical wake-up signal. You can then plug the connector back in and move on to the next control unit on the
fi ber-optic bus. Unplug that connector, turn the ignition key back on, and watch for the same bl inks. Keep moving on through the next cont rol units until you no longer observe the bl inking. Remember, the Fiber-optic net work is in series. So, the control unit that you just unplugged is not the one you're testing. You're look ing for the output signal from the control unit before it's on the bus. If you no longer see the wake-up call, it is either not coming out of the control unit before it's in the network, or the cable has a break in it.
You can purchase a special fiber-optic loop tool, which is sort of li ke a jumper w ire. You can plug it into the fiber-optic connector of each control unit
the fiber-optic network with an electrical
wake-up line. This signal is generated by the master control unit, but it is conventionally wired in parallel. The wake-up signal is sent and each control unit answers on this wakeup line. The control unit that does not respond has fa iled. This is how the master control unit senses the system fai lure and sets diagnosti c
trouble codes. Veri fy power and ground and you have diagnosed the problem.
EVOLUTION, NOT REVOLUTION The only rea l difference between the D2B
bus and the next evolutionary stage, the
MOST (Media Oriented System Transport), is the communication protoco l. The diagnosis is exactly the same. Use XENTRY to compare the elec trica l wake-up signal and compare it to the fiber-optic network. The two special tools for the D2B and MOST sys tem are inexpensive and available from your local Mercedes-Benz dealer's part department -- remember, they 're
happy to help. I
on the network. If you turn the key on and the system starts to work, then the control unit you just bypassed is
. Transport Screvv Rernova l Advice
the problem. This does not mean the control unit is necessaril y bad. You sti 11 need to verify power, g rounds, and the wake-up signal at that control unit, starting with the fuses that power it up.
Mercedes-Benz has made diagnosis even easier by backing up
24 Mercedes-Benz StarTuned
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The MOST bus is programmable with XENTRY software. Remember, if you want to add a component to the MOST bus you need to go into the MOST master and change the coding for the new configuration. You must get the order right in the fiber-optic loop for stable MOST bus operation.
Mercedes-Benz Mobil 1 Product Name Part Number Quantity Product Description Recommended Consumer Applications
MercedeirBenz SPEC.
BQ 1090144 Bulk - No Equipment Mobil 1 BQ 1090162 6/1 Quart Cases
Fully synthetic formulas designed Low SPAsh. Available at most MB dealers Formula M 5W-40 specifically for gasoline passenger cars
BQ 1090151 55 Gallon Drum
Genuine A0009898301 USB6 12x1 Quart Cases · Mercedes-Benz Oil Fully Synthetic formula specifically . . MB 229 .5 A0009898301 USBB 55 Gallon Drum designed for Mercedes-Benz engines Mercedes-B.e.nz Engines that require Specification that require the 229.5 Specifica tion 229·5 Specification Oil SAE 5W-40 A0009898301 USB9 Bulk - No Equipment
BQ 1090010 Bulk - No Equipment Fully synthetic formulation designed Porsche A40. Many European vehicles.
Mobil 1 OW-40 BQ 1 09 0015 6/1 Quart Cases to meet the requirements of many European vehicles HT /TS applications.
BQ 1090016 55 Gallon Drum
Mobil 1 ESP BQ 1090135 Bulk - No Equipment Formula M 5W-40 Advanced full synthetic formulas designed specifically for diesel Low SPAsh. Available at most MB dealers
BO 1 09 0142 6/1 Quart Cases passenger cars that have particulate
BQ 1 09 0143 55 Gallon Drum filters
Higher viscosity, advanced full synthetic
BQ 1 09 0134 6/1 Quart Cases formula designed for performance Porsche A40. HT /HS applications. vehicles
Extra high performance automatic Recommended tor use in Mercedes-Benz BO 1 09 0166 55 Gallon Drum transmission fluid formulated with selected HVI base oils automatic gearboxes
Advanced full synthetic formulas Low SPAsh. Available at most BQ 1 09 0165 12x1 Liter Cases designed specifically for passenger car MB dealers. diesels that have particulate filters
1 AdBlue• 1/2 Gal. A 000 583 0107 1 /2 Gallon Bottle Non-toxic solution that transforms Recommended for use in Mercedes-harmful Nitrogen Oxide (NOx) emissions Diesel Exhaust Fluid BQ 1470002 55 Gallon Drum from diesel-powered vehicles into Benz, Volkswagen + BMW AdBlue• (DEF)
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BQ 1090017 6/1 Quart Cases Advanced full synthetic formulation designed to meet the requirements Vehicles that require 5W-30. Corvette
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BQ 1 09 0019 6/1 Quart Cases
Mobil 1 lOW-30 BQ 1090020 16 Gallon Keg Advanced full synthetic formula designed for domestics and imports Vehicles that require 5W-30 or lOW-30
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Mobil 1 5W-20 designed to meet the requirements of Vehicles that require 5W-20 BQ 1090084 55 Gallon Drum many newer vehicles including Hondas,
Eords Cbr>!slers aad aewer Iaimtas BO 1 09 0169 6/1 Quart Cases Advanced full synthetic formulation Most vehicles that specify OW-20 (newer
Mobil 1 OW-20 AFE designed for enhanced fuel economy Toyotas and Hondas), 5W-20 and certain BQ 1 09 0168 55 Gallon Drum and cold weather performance hybrids
Mobil 1 OW-30 AFE BQ 1090174 6I1 Quart Cases Advanced full synthetic formulation Most vehicles that specify 5W-30 or designed for enhanced fuel economy and cold weather performance lOW-30
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vehicles levels
Mobil 1 15W-50 BQ 1090023 55 Gallon Drum Boosted, higher viscosity, advanced HT /HS applications. Racing and Flat full synthetic formula designed for performance vehicles tappet applications
Mobil 1 Gear Oil Exceeds the most severe service SUITABLE for use in modern high
(Mobil 1 Gear Lube BO 1 09 0085 12/1 Quart Cases requirements in both conventional and performance automobiles like SUV's,
75W-90) limited slip applications Vans and Light duty trucks requiring API GL-5 level performance
M ercedes-Benz automobiles are designed to perform on
the most challenging roads and conditions. Shouldn't the oil
used in Mercedes-Benz engines do the same? We think so.
That's why Mercedes-Benz and Mobil 1 have partnered to
offer an unbeatable combination of total engine performance
and driving luxury.
Please have a look at our oil portfolio which is available
through your local Mercedes-Benz dealer. Our dealers are able
to offer you a wide variety of oil grades at competit ive prices.
Product Name Part Number Quan tit Product Descri tlon Mercedes·Benz SPEC.
Mobil 1 Gear Oil Exceeds the most severe service (Mobil 1 Gear Lube BO 1 09 0085 12/ 1 Quart Cases requirements in both conventional and 75W-90) limited slip applications
BO 1 09 002464 Bulk - No Equipment Formulated from quality base stocks
BO 1090171 12/1 Quart Cases combined with modern performance
Mobil Special 5W-30 additives to give the engine the expected
BO 1 09 003064 55 Gallon Drum protection and performance under a wide variety of operating conditions
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BO 1090172 12/1 Quart Cases combined with modern performance
Mobil Special lOW-30 additives to give the engine the expected
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BO 1090173 12/ 1 Quart Cases combined with modern performance
Mobil Special lOW-40 additives to give the engine the expected
BO 1 09 004464 55 Gallon Drum protection and performance under a wide variety of operating conditions
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BO 1090170 12/1 Quart Cases combined with modern performance
Mobil Special 5W-20 additives to give the engine the expected
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Formulated from quality base stocks combined with modern performance
Mobil Special 20W-50 BO 1 09 004664 55 Gallon Drum additives to give the engine the expected protection and performance under a wide variety of operating conditions
BO 1090053 Bulk - No Equipment Extra high performance diesel engine
BO 1 09 0058 12/ 1 Quart Cases oils that help extend engine life in
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performance in modern, high-output, BO 1090060 55 Gallon Drum low-emission engines including those
with Exhaust Gas Recirculation (EGR)
Mobil Delvac 1300 and Aftertreatment Systems with Diesel
Super 10W30 BO 1090086 Bulk - No Equipment Particulate Filters (DPFs) and Diesel Oxidation Catalysts (OOCs)
BO 1 09 0051 4 / 1 Gallon Cases Fully synthetic supreme performance heavy duty diesel engine oil that helps
Mobil Delvac l 5W40 extend engine life while providing long
BO 1090052 55 Gallon Orum drain capability and fuel economy for modern diesel engines operating in severe applications
BO 1 09 0078 60/14 oz Cartridge
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resistance to water contamination BO 1090098 40/ 14 oz Cartridge
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specifically for limited-slip differentials
Recommended Consumer Applications
SUITABLE for use in modern high performance automobiles like SUV's, Vans and light duty trucks requiring API GL-5 level performance
Recommended for gasoline fueled automobiles and light duty trucks requiring an API SN/SM/SL/SJ
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Specifically recommended for the latest low-emissions, high performance diesel applications equipped with aftertreatment systems using Diesel Particulate Filter (DPF) and Diesel Oxidation Catalyst (DOC) technologies
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Bumper Tech Mercedes-Benz Safety Systems Help Avoid Accidents and Significantly Change Bumper Repair
Mercedes-Benz safety technology features state-ofthe-art sensors that constantly monitor the position of the vehicle relative to other vehicles and obstacles. Software analyzes sensor data and, if necessary, sends commands to various safety systems to alert the driver to a potential problem. If the driver does not respond quickly, the system can pre-pressurize the brake master cylinder, reduce speed, or stop the vehicle, apply the brakes in a manner that prevents an unsafe lane change, or backing into an alreadyoccupied space, and adjust seat belts, seat position, head rests, and other supplemental restraint components in preparation for a possible collision. All of this is made possible by short- and longrange radar and other sensor technologies. The safety sensors are embedded in or attached to the bumper and front grille, which makes bumper repair after a collision very different from the procedures of only a decade ago.
There are six Parktronic sensors in the front bumper of this 2010 GL 450. The small round sensor heads blend beautifully into the bumper, and enable several different safety functions, including adaptive cruise control, lane departure warning, and other collision avoidance systems.
28 Mercedes-Benz StarTuned
Mercedes-Benz safety technology features
state-of-the-art sensors that constantl y monitor
the posit ion of the vehicle relati ve to other vehicles and obstacles. Software analyzes
sensor data and, i f necessar y, sends commands
to various safety systems to alert the driver to a potential problem. I f the driver does not
respond quick ly, the system can pre-pressu ri ze
the brake master cy linder, reduce speed, or
stop the vehicle, apply the brakes in a man ner that prevents an unsafe lane change, or backing into an already-occupied space, and
adjust seat belts, seat position, head rests,
and other supplemental restraint components
in preparat ion for a possible collision. A ll of
this is made poss ible by short- and long-range
radar and other sensor technologies. The safety
sensors are embedded in or attached to the
bumper and front gri lle, which makes bumper
repair after a col lision ver y different from the procedures of on ly a decade ago.
Automotive sa fety st rategies have historica lly
been passive in nature. Seatbelts, ai rbags,
bumpers, and other devices sought simpl y to
reduce the impac t of a collision on the vehicle and its passengers. Over the past 15 years or
so, however, new safet y technologies have been
developed that emphasize acc ident avoidance,
and in more active ways than could be imagined
on ly a few decades ago. Much of th is new safety tech no logy features h igh-tech sensors that see th rough the Mercedes-Benz front and rear
bumpers, so bumper repair is no longer a simple straighten, patch, and re-pain t job.
For example, ordinary cruise control keeps
driv ing speed at a pre-set pace, but Adapt ive
Cruise Control helps maintain the desired distance between the vehicle and the one immediately ahead. This function is enabled by
the Mercedes-Benz Distronic Plus system.
Distronic Plus features a combi nation of
short-range radar sensors beh ind the bumper
cover and a long-range sensor in the front
gri I le. These sensors together measure the distance between vehicles, and al low the
electronic logic to determ ine whether or not
that gap is decreasing. The software assesses
how quickly the gap is decreasing and
determines how much braking power is needed
to restore the gap to the preferred length. The
system then progressively applies the brakes to slow the vehicle and restore the gap to the desired distance.
There are four Parktronic sensors in the rear bumper of this 2010 GL 450. Parktronic sensors in the rear help with lane departure warning and Parking Assist functions. There are similar sensors in the front bumper on many Mercedes-Benz models.
A vehicle traveling at 50 k mh (31 mph)
covers 20 m (65 ft.) in two seconds. Adaptive Cru ise Control aler ts the dr iver to a dangerous situation v ia flashing lights in the dash or Head
Up Display, but does not wait for him or her to
take action. Mercedes-Benz Distronic Plus radar
technology is never vu lnerable to the things
that somet imes distract humans from the road
ahead, and it responds faster and w ith more
precise application of braking force than any dri ver could, no matter how sk illed.
Mercedes-Benz Pre-Sa fe Brake is another
example of active safet y st rategy. Pre-Sa fe
Brake sensors scan the road ahead for potential
problems. If they detect a vehicle a head
slowing, stopped, or crossing its path, or "see" pedestrians or other obstacle, the system alerts
the dri ver.
Pre-Safe Brake simultaneously initiates up
to 40% of the available braking power. When
the driver brakes, the appropriate amount of braking pressure is instantly applied, all the way up to 100% if the driver so chooses. And
should the driver fa il to respond, the system will apply full braking on its own, to help
avoid or reduce the intensity of a coll ision.
Independent studies show that th is precharg ing of the brakes shaves enough off of the
driver 's reac tion ti me to effective ly increase
the occupant survival rate in an accident by 10 to 15%.
This abili ty to take control of vehicle brak ing
is only part of the Mercedes-Benz act ive sa fety
strategy. Pre-Safe also adjusts vehicle restra int systems w ithi n mil liseconds, to prepare for
a potent ial acc ident. Tt tightens the front seat
belts, adjusts the front head restrai nts and
passenger seat, and, i f the vehicle is equ ipped
w ith the Mercedes-Benz Memory System, can
even close the w indows and sun roof.
HIGH-TECH BUMPER CARE Suppose a customer comes in w ith the
complaint that after a minor front collision, the
Adapti ve Crui se Control no longer works. You'll
need to add to your t raditional coll ision-repair
knowledge in order to help this motorist.
Mounted in the front bumper cover on vehicles eq uipped with the Parktronic system are six u ltrasonic sensors. They can not
Collision avoidance sensors sit behind plastic grille covers in each side of the front bumper of this 2014 ML 350.
30 Mercedes-Benz StarTuned
>
be repaired. If one has been impacted in a
collision, it must be replaced. Even if on ly a few scratches penetrate the paint and dig in to the
sensor surface, complete replacement of the
sensor is required.
If the repair i nvolved replacement of the
Distronic (DTR) control un it, the sensors that monitor rotationa l speed, yaw rate, and latera l
acceleration, or of the steering column tube module, the DTR control unit must be initialized
and recalibrated.
Another possible cause of problems w ith
the shor t-range radar sensors is the seal ing
ring where the sensor seats into the bumper.
The sensors and con nec tors are designed to be waterproof, and to resist a high degree
of v ibration and shock. If the sea ling ring is
damaged, it may al low vibration or moisture to
overwhelm the sensor. A damaged seali ng r ing
should be replaced.
PAINTING BUMPERS Have you had a customer bring in a vehicle
w ith the complaint that after another shop
repai red a bumper, the backup assist,
lane depar tu re warning, or other collision
avoidance system no longer works? It could be the paint job.
When painting the bumpers, it is important
to ensure that the paint coat on the short-range
radar sensors is of only minimal thickness.
Too thick a coat can lead to malfunctions
because the sensors see it as an obstacle in the vehic le's path, rather than as merely excessive paint thickness. The system will respond by
either keeping the warning lights or beepers
constantly on, or shutting down completely after
a certain amount of t ime to prevent full-time
appl ication of the brakes and activation of key elements of the supplemental restraint system.
The maximum paint thickness allowed at
the sensors is the primer and two coats of
paint (color and clear). Primer, color, and clear
together count as one refi nish, but the painter
MUST be mind fu I of keeping each coat as
minimal as possible.
We shou Id mention that pre-painted sensors
are avai lable for cer ta in popular colors.
When it detects an obstacle (like the two-by-four stud we placed in front of this vehicle), the Parktronic system begins flashing red lights in two places on the dashboard.
June 2014 31
The scuffing over the Parktronic sensor in the rear bumper of this 2010 GL 450 is enough to require sensor replacement.
PLASTIC: REPAIR OR REPLACE? Damage to bumper covers and protective
bumper strips in the form of cracks, holes, and scuff marks deeper than one millimeter can be fi xed using the Teroson plastics repair k it (see the approved materials I ist at
http://porta l.aftersa les.i.dai m !er.com in the
paint technology guidelines sect ion).
The Teroson k it includes a cleaner that removes dirt, grease, and other contam inants, a
primer that prepares the surface fo r fi ller, a t wo
part adhesive filler, and a glass fi ber mesh. The filler hardens in 15 minutes under an in frared
lamp. The fi ber mesh rei nforces the adhesive to
help resist repair fa ilure due to expansion and
contraction of the plastic over ti me.
With six sensors in the front and four in the rear bumper, it is easy for filler that is feathered out from the damaged spot to overlap one or more sensors. The add it ion of primer, basecoat,
and clearcoat can then quick ly build up to levels in excess of paint thickness max imums, renderi ng the affected sensors inoperable. If the damaged area is close enough so that the fi ller would overlap the sensor, replace rather than repair the bumper.
32 Mercedes-Benz StarTuned
Mercedes-Benz short-range ultrasonic Parktronic sensors insert directly into the back of the plastic bumper, and include a seal that helps them resist road-induced vibration and shock.
BUMPER BASICS A MJrcedes-Benz bumper consists of three
or four basic components: a decorative plastic
bumper cover, a foam impact absorber bar, a steel or alu minum reinforcement bar, and, depending
on the vehicle model, outer protective strips.
The foam impact absorber bar is located
between the decorative cover and the metal reinforcement. Its purpose is to compress and
absorb some of the damage in a low-impact
col lision. Be careful when handl ing the foam
inserts, as they snap easi ly.
The metal reinforcement bar attaches to the
front crossmember and is designed to absorb some of the energy of a low-impact collision.
In a two or three mile per hour "parking lot"
incident, the damage to the vehicle may be
limited to the bumper cover, impact absorber, and reinforcement bar.
The Mercedes-Benz reinforcement bar
is a si ngle-use component, and ca nnot be
repa ired. If it has been damaged, it must
be rep laced.
Some models feature outer protective
str ips. A lthough primari ly decorative,
t hey are sacrificial plast ic p ieces. They are inexpensive and snap on using c li ps, so they are easil y replaceable i n the event of
mi nor impact or scratch damage.
BOLT-ON MODULES Front and rear modu Jes absorb and deflect
some of the impact energy of a col I is ion
away from va luable mechan ical components.
The modu les bolt on to the upper and lower longitudinal members (frame rai ls). The
bolt-on design helps reduce repair ti me and
cost ver sus a welded fu 11 frame.
An aluminum reinforcement bar is built onto the crossmember of the front module. A foam impact absorber sits between the decorative bumper cover and the reinforcement bar.
June 2014 33
ADDITIONAL CONNECTORS IN MERCEDES-BENZ FRONT BUMPERS
• Washer Flu id Reservoir - On vehicles
w ith a Headlamp Washer System, you
must detach the electrica l and fluid
hose connections from the windshield
washer fluid level indicator switch and
pump, and remove the Washer Flu id
Reser voir in order to access and replace
the front bumper.
• The Outside Temperature Sensor - clips to
the front bumper, and must be disconnected
in order to remove the bumper.
THE FEW, THE PROUD, THE KNOWLEDGEABLE
These new safety features a re based on
cutting-edge sensor technology and are now
being seen for the first time by many coll ision
repair technicians. Di g into your Mercedes-Benz
train ing in formation and learn how the systems
work. You'll find that k nowing where a sensor
is located, how it must be posit ioned to "see" so
it can accurately esti mate the vehicle's position
relative to nearby objects, and how your repair
prep and painti ng procedures must adjust to
avoid in terference w ith sensor operat ion w i ll
make you an in-demand ex pert in your market. I
The Mercedes-Benz front module bolts onto the upper and lower frame rails. In a low impact (up to eight mph) accident, the front module may absorb all of the collision energy as it crumples, leaving the frame rails undamaged. In that scenario, repair involves simply bolting on a new front module.
34 Mercedes-Benz StarTuned
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