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4 GEARS November/December 2004

In the battlefield, surgeons arefaced with making quick deci-sions… decisions that can turn

their day from joy to drudgery. Timepresses against them as they’re forcedto make precise decisions to further thepatient’s recovery.

Here’s the setting: Through thewindow we see an ambulance (towtruck) bringing in yet another fallenpatient. The atmosphere is tense as weget the word. The patient has fallen(failsafe on a 41TE); how do we pin-point key issues that will make or breakcritical operating procedures withoutleaving too much room for error orwasted time?

In this issue of Doctor, Doctor,we’ll look at solenoid codes that areelectrical, verses pressure switch codesthat can be either electrical orhydraulic. Past test procedures havetaken technicians to areas that can notonly confuse the diagnosis, but wastevaluable time. The setting is all toofamiliar; these decisions need to bemade daily as the surgeons (techni-cians) plan out their workday, because,time is money. The question has to be:What is a solenoid code, and what is apressure switch code? Let’s take a lookat these circuits…

Solenoid CodesSolenoid codes are classified as an

electrical malfunction determined by

the transmission controlmodule. Here are the sole-noid trouble codes:

41 (P0750) LR solenoid42 (P0755) 2-4 solenoid43 (P0760) OD solenoid 44 (P0765) UD solenoid

These codes can becaused by several differ-ent conditions, but we cannarrow them down a bit.Depending on the vehicleyou’re working on, you’llbe able to use these teststo identify solenoid prob-lems.

We’ll be dealing with a patientwhose heritage is A604 (41TE). Here’san example from a real-life story: Thevehicle owner started his car and left itidling in the driveway (warming upbecause of cold weather). The heater ison high fan (because it’s freezing out),the interior dome light left on to pro-vide additional safety when he comesback, and the headlights are on highbeam, lighting the perimeter for clearpassage back to the vehicle.

The owner finishes his cup of cof-fee, jumps in the car, and BAM! Thevehicle is in failsafe (MIL is lit) with asolenoid code in memory. A call goesout to the medical center (transmissionshop), which responds by sending the

ambulance (tow truck) to pick up thecar and bring the patient to the center.

First things first: a scan tool isinstalled to check the system. Sureenough, code 41 is present. The doctordocuments and clears the code; during aroad test, the code doesn’t reappear. Infact, the car runs perfectly, the way itwas designed to. Asking the right ques-tions, the doctor checks to see how thishappened. It turns out the problem wascaused by extended periods of idlingwith excess loads on the system.

Since this is an electrical code thatoccurs during extended periods of lowengine RPM, the test requires simulat-ing these conditions. The car is leftidling with as many accessory loads on

by Randall Schroeder

Figure 1

DOCTOR DOCTOR…It hurts when I shift!

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as possible, to simulate warmup condi-tions. Sure enough, the code sets.Further investigation reveals that thecharging system simply isn’t keepingup with the demands of the electricalsystem. While idling in the bay, charg-ing levels dropped to 12 volts. This wasenough to keep the engine running, butnothing else.

It turns out the alternator belt wasloose and barely driving the pulleys, sothe alternator simply couldn’t do itsjob. Once the belt was tightened, thesystem worked the way it was designedto, and the code didn’t return.

Sound simple? They’re not all assimple as this, but they can be. In thissystem, solenoid codes are set when thecontroller (monitoring the solenoid cir-cuit) de-energizes the solenoid and dis-covers that the inductive spike createdwhen the solenoid’s magnetic field col-lapses falls either too short or too highfor the module’s programming (figure1). The spike’s voltage level must fallbetween a preset range.

Here’s another way to look at it: ifthe voltage spike were a skyscraper

with, let’s say, 10floors, and eachfloor represents anincreasing voltagelevel, the spikemust be betweenfloor 4 and 6 (fig-ure 2). Any higher(7 or above) orlower (3 or below),and it sends a failsignal (code sets).The spike must bebetween theparameters pro-grammed into themodule.

Let’s look atthe four main problem areas thatcan cause this signal to be out ofrange, and cause a code to set.

Problem Area 1: ChargingSystem

If the charging system does-n’t supply enough voltage, thespike will be too low. An exam-ple of this is the loose alternatorbelt. Generally speaking, thecharging system should developover 13 volts; usually between 14and 15 volts.

On the other hand, if the system isovercharging — 16 volts or higher —the spike will be too high, and will alsoset a code.

Problem Area 2: TransmissionRelay

Burnt contacts in the transmissionrelay can supply low voltage to the


Advanced Triage Training for Solenoid Codes

Figure 2

Figure 3A

Figure 3B

Figure 4

Here’s another way to lookat it: if the voltage spikewere a skyscraper with,let’s say, 10 floors, and

each floor represents anincreasing voltage level,

the spike must be betweenfloor 4 and 6 (figure 2).


sonnax1.qxd 11/2/04 2:22 PM Page 7

solenoids. This creates the same situa-tion as a low charging voltage, as far asthe module is concerned. In either case,the spike will be too low, and the mod-ule will set a code.

Problem Area 3: Wiring Harness or SolenoidBody

There are a number of differentpossible problems covered within the

wiring harness or solenoid body, anyone of which could cause low voltageand set a code:• Damaged wires from the relay to

the solenoid block.



Figure 5


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• Switched voltage pins at the module.• A problem in the wires from the

solenoid block to the transmissioncontrol module.

• Loose connections on the wiringharness.

• Broken or incomplete wires con-nected to the terminals inside theconnectors.

• Faulty solenoids inside the sole-noid body (improper resistance).

You could even be dealing with afaulty transmission module. Keep inmind these conditions are only for deal-ing with electrical-only solenoid codes.

Problem Area 4: TransmissionModule

It’s possible for the module itself toreduce the voltage levels to the sole-noids, and create the conditions to set asolenoid code. Always check systempower and ground to the module beforecondemning the module itself.

Pressure Switch CodesPressure switch codes can be

caused by electrical or hydraulic problems. An over- or underchargingvoltage supply won’t set a pressureswitch code, even if the problem some-how made it past the solenoid watch-dog. Only voltage signal on the moni-tored pressure switch wires — or the

lack of a voltage signal — will set apressure switch code.

Let’s take a look at the pressureswitch circuit as we get into simple test-ing. The pressure switch codes are:

21 (P01780) OD pressure switch22 (P1781) 2-4 pressure switch23 (P1782) 2-4/OD pressure

switch circuit24 (P1783) LR pressure switch

circuit25 (P1784) LR/OD pressure

switch circuit26 (P1785) LR/2-4 pressure

switch circuit27 (P1786) All pressure switch

circuits

Which codes set depends on whenthe circuit failed: the computer moni-tors the three pressure switch wires.These pressure switches are normallyopen, and they close (ground) whenpressure applies to the switch. Workslike a light switch: on-off… voltage/novoltage.

When the switch is open, the mod-ule sees system voltage originatingfrom the transmission relay, and sup-plies it to the solenoid/switch block.When pressure is 12 PSI or lower in thecircuit, the switch remains open;switched voltage is present at one ormore of the module pins. When pres-sure rises to at least 13 PSI, the switchcloses, grounding the circuit. Voltage

drops to less than 1 volt at the module.Since it’s a switch, all the module wantsto see is this change from high to low;on to off; 12 volts to zero.

A problem appears if a crossleakdevelops inside the transmission; if thepressure rises to 13 PSI, it’ll close theswitch and set one of the switch codes.And a crossleak can be difficult prob-lem to track down. You’ll need a goodoil schematic and a set of pressuregauges; refer to figures 3a-3b for pres-sure tap locations.

If a switch wire is pinched toground or broken, the circuit voltagewill behave as though the switch closedhydraulically: The module will neversee voltage, even when the switch isopen. This is why these codes can indi-cate either electric or hydraulic failures.The codes set when the module sees animproper voltage signal for the com-manded range.

Isolating and Testing theCircuits

Always begin by making sure thebattery is fully charged, and the con-nections are clean and tight. Never tryto test the electrical system when a bat-tery looks like the one shown in figure4. Battery no-load voltage should be atleast 12.45 volts before continuingthese tests.

Once you’re sure the battery isokay, check the charging system. Withthe engine running, turn every load inthe vehicle on (lights, fans, radio, A/C).Charging voltage should be between13.5 and 15.0 volts at idle. If the batteryand charging system are okay, you cancontinue to the next phase of testing.

A good way to make sure that thecodes you’re dealing with aren’t beingcaused by a faulty relay is to replace therelay with a new one and retest the sys-tem (scan for codes). Some sources rec-ommend that you simply change therelay with a similar one, such as thebackup light relay. But what if thatrelay’s bad too? Always make this testwith a new relay. If codes go away withthe new relay, there’s no need for fur-ther testing: simply order a new testtool (relay) for your toolbox.

But if the problem’s still there witha new relay, here’s how to test the restof the system:



Figure 6


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• Get an accurate wiring diagram(figure 5) and identify the circuitsyou’ll be testing (figure 6).

• Remove the transmission relayfrom its receptacle. It may be nextto the transmission module or in arelay center, depending on the yearand model you’re working on.

• Disconnect the negative cable fromthe battery and unplug the trans-mission control module wire har-ness (figure 7). Any time youunplug a module, always discon-nect battery power to prevent dam-aging circuits.

• Locate the wires to be tested at themodule connector, then reconnectthe negative battery cable.

You’re going to test for voltage throughthis path:

• system voltage to pin 56 (KeepAlive Memory; KAM)…

• going through the relay circuit(jumper installed; figure 8)…

• to the switch voltage pins at themodule (16 and 17)…

• down to the solenoid block (pin 4on the solenoid block)…

• through the solenoids and switch-es…

• ending up at solenoid ground pins20, 19, 60, and 59 on the module,and…

• pressure switch pins 50, 47, and 9on the module.

You’ll perform all of these testswith a digital volt-ohmmeter (DVOM).You won’t need to turn the key on, assystem voltage should always be pres-ent in the KAM wire. Chrysler’s used avariety of relays, so always refer to a

connector chart to make sure you’rejumping the correct wires for this test.Figures 9 shows five common relay terminal patterns for reference.

• Connect your voltmeter negative (-)lead directly to the negative batterypost.

• Touch the positive lead to the pos-itive (+) battery post to measurethe reference voltage level (figure10).

• Touch the voltmeter positive (+)lead to all the pins in the voltagesupply circuit of the module (56, 16, 17, 20, 19, 60, 59, 50, 47, and 9) (figure 11).

Every one of these pins shouldhave system voltage for the first part ofthis test. If any of the voltages is lowerthan system voltage, backtrack throughthe circuit till you find the source of thevoltage drop. Repair as necessary.

For solenoid codes, you should goone step further and energize the sole-noids using your meter set for measur-ing amperage. To do this test:• Remove the ground test lead from

the negative battery post.• Selecting amperage (amp) scale on

your meter; switch the positivelead to the heavier amperage sock-et; usually 10 or 20 amps.

• Connect the positive test lead tothe computer connector pins 20,19, 60, and 59, one at a time.

• Ground your meter’s negative (-)lead, and measure the current drawfor each of the solenoids (figure12).


A good way to make sure that

the codes you’re dealing with

aren’t being caused by a faulty

relay is to replace the relay

with a new one and retest the

system (scan for codes).

Figure 8

Figure 7


Install JUMPERwire across pins

at EATX relay


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Figure 9

Five common

relay terminal patterns

for reference.


Each solenoid should draw around6 amps; higher current draw indicates ashort in the unit or solenoid windings.Lower indicates high resistance or anopen internally. But if all the voltagesare present at the connector and theamp draw is within specs, the wiringand solenoids are okay. The most likelysource of the problem is the module.

Before changing any module,always check for power and grounds.Check for system voltage supplied tothe module (pins 8 cranking and 11 run-ning). And make sure the computergrounds (pins 53, 54, 57, 58 and casing)have no more than 0.02V with theengine idling. Everything must bereconnected for this test; both the com-puter connector and relay. Once you’veconfirmed all of the circuits, replace themodule.

Pressure switch code tests will bethe same as solenoid code with oneexception: Never try to check currentdraw through the switches!

Keep in mind that the switchesclose at 13 PSI. Start by testing theswitch voltage with the engine off.

Since the engine isn’t running, thereshouldn’t be any pressure in the unit, soall three switches should be open. Withthe switches open, you should see volt-age at the computer connector.

If any of the switches isn’t provid-ing voltage to the module, the switchmay be stuck closed (faulty switch) orthe wire is broken or grounded betweenthe solenoid block and the transmissionmodule (bad wire harness). You’ll needto perform a second test at the pins inthe solenoid block to see if the problemis in the wires.

But if the switches are all open andproviding voltage to the module, yournext step is to see if the switches canclose. To do that, you’re going to openthe transmission pressure taps and sup-ply pressure using shop air.• Remove the pressure taps.• Block the wheels or raise the car to

keep the vehicle from rolling.• Unlock the steering column, and

shift the transmission into drive.• Supply air to the pressure tap on

the transmission that leads to theswitch being tested.

GEARS November/December 2004 15

Figure 10

Touch the positive lead to the pos-itive (+) battery post to measure

the reference voltage level

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As the switch grounds (13 PSI orgreater in the circuit), voltage shoulddrop to 0.00 volts. If there’s no change,the switch is stuck or damaged (faultyswitch).

If the switch circuits are workingcorrectly, you’ll have to check the pres-sures, to make sure you aren’t dealingwith a crossleak in the transmission.

Pressure TestingReconnect all connectors and rein-

stall the relay, so the computer systemis in control of transmission operation.Install a pressure gauge in one pressuretap, and reinstall the plugs in the rest ofthe taps. Monitor the pressures whiledriving; you should have less than 5PSI in any oil circuits that aren’tapplied: Low/Reverse: Pressure in park,

reverse, neutral and drive 1st gear— switch closed (open in all otherranges).

2-4: Pressure when in 2nd and 4th

gear — switch closed (open in allother ranges).

OD: Pressure in 3rd and 4th gear —switch closed (open in all otherranges).

If there are no signs of internaltransmission crossleaks causing pres-sure to close the switch before its time,check for proper power and grounds tothe module. If power and ground levelsare correct, replace the module.

In most cases, these tests shouldtake no more than about 15 minutes;remember, time is money in the techcenter. Until next time, keep thosetransmissions shifting in a healthymanner.

The Doctor…



Figure 11

Figure 12

In most cases, thesetests should take nomore than about 15 minutes; remember,time is money in the

tech center.

Touch the voltmeter positive (+) leadto all the pins in the voltage supplycircuit of the module (56, 16, 17, 20,

19, 60, 59, 50, 47, and 9).

Ground your meter’s negative (-)lead, and measure the current draw

for each of the solenoids.


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