Are you using the fullpower of your scantool? My experiencehas shown that manytechnicians use a scantool only to retrieve di-

agnostic trouble codes (DTCs) andlook at parameter data, while overlook-ing other powerful features. One ofthese overlooked features is bidirec-tional control, and most enhanced scantools have this capability.

Bidirectional control is a genericterm used to describe sending and re-ceiving information between one deviceand another. The vehicle engineers re-sponsible for designing computer con-trol systems programmed them so ascan tool could request information orcommand a module to perform specifictests and functions. Some manufactur-ers refer to bidirectional controls asfunctional tests, actuator tests, inspec-tion tests, system tests or the like. Reini-tialization and reprogramming also canbe included in the list of bidirectionalcontrols.

This article will explain the benefitsand limitations of bidirectional controlsand demonstrate how they can be usedin the diagnostic process. Specific scantools are mentioned for illustrative pur-poses only. No attempt was made toevaluate every available tool.

The scan tool is the primary bidirec-tional control device and could actuallybe called a bidirectional tool, becauseit sends information to, and receivesinformation from, vehicle control mod-ules. For example, in the case of OBDII generic information Mode 1 (whichrelates to data parameters), the scantool user initiates a request for infor-mation from the powertrain controlmodule (PCM), and the PCM re-sponds by sending the informationback to the scan tool for display. Mostenhanced scan tools also have the abili-ty to actuate relays, injectors and coils,perform system tests, etc.

Fig. 1 on page 40 shows severalscreen captures taken from a 2004Honda Civic, using the Teradyne Pock-et Tester. The bidirectional controls forthis vehicle are listed under the Inspec-tion Menu and, as you can see, manyuseful tests are available. The techni-cian can turn the fuel pump on and off,

cycle the a/c clutch on and off and per-form an evaporative emissions leak test.The options programmed into both thevehicle and the scan tool will deter-mine the range of options available.

This brings up a key question: Arethere differences among scan tools?Everyone knows the answer is yes. De-signing and building scan tools is a diffi-cult process for vehicle manufacturersand aftermarket scan tool manufactur-ers. Automakers spend lots of time andmoney designing the best possible diag-nostic tool for their product lines. Costis a consideration, of course, but theydon’t have the luxury of deciding whatto leave out. The diagnostic platformmust communicate with and diagnoseall possible systems. Aftermarket scan

tool manufacturers, on the other hand,have a slight advantage in knowing whatthe factory scan tool is capable of doing.But these companies have several issuesto consider that don’t concern theirOEM counterparts. Here are a couplethat relate to bidirectional controls:

•Is the information available fromthe vehicle manufacturer to build an af-termarket scan tool? If the vehicle man-ufacturer makes the design informationfor scan tool bidirectional control avail-able, in most cases building an after-market version is simplified. But thisdoes not mean it will be easy or cost-ef-fective. Bidirectional controls are themost difficult feature to implement.Two issues are liability and safety. Forexample, it would not be wise for a

38 April 2005

BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAYBY BOB PATTENGALE

Maintaining an up-to-datearray of diagnosticequipment will cost a prettypenny. But it’s a downrightwaste of money if you aren’texploiting the full capabilities ofthe equipment you already have.

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technician to command an increase inengine speed if the transmission were ingear and the brake not applied. Toavoid damage to the vehicle and/or per-sonal injury, some type of protectionmust be implemented. In some cases,this protection was programmed intothe vehicle module; in others, the pro-tection was designed into the scan tool.An aftermarket scan tool manufacturerneeds to know this information.

•What are shop owners and techni-cians willing to pay for an aftermarketscan tool? Each scan tool maker mustevaluate the cost involved in building ascan tool and determine the optionsmost important to technicians. In thepast, most of the computer technologywas designed into engine control sys-

tems, so the primary focus was on build-ing a good engine diagnostic tool. Evenwith this focus, many aftermarket scantools do not include all the parametersand tests available in the factory scantool. Many shop owners and technicianshave made the decision to purchase thefactory scan tools to ensure all the infor-mation is available. This is becomingmore of an issue when dealing with non-engine control systems—e.g., antilockbrakes (ABS), supplemental restraintsystems (SRS), climate control systems,electronically controlled transmissions,body control systems and the like. After-market scan tool companies need to in-crease the level of coverage built intotheir equipment to stay competitive.

Aftermarket scan tool makers have

done a good job of working throughthe issues. But don’t be surprised orupset if you pick up a factory scan tooland find it has features or tests notavailable on your aftermarket tool.Each is built for a different market andtherefore must satisfy different objec-tives and needs.

Getting Down to DiagnosticsWhen properly utilized, bidirectionalcomponent and system tests can sig-nificantly reduce your diagnostic time.Consider a no-start situation. You’veconnected a fuel pressure gauge, cy-cled the key and cranked the engine,but no fuel pressure was measured. Atthis point you don’t know if the prob-lem is a component, a circuit or com-

39April 2005

mand-related. The scan tool you’re us-ing has a fuel pump command avail-able. Using the scan tool, commandthe fuel pump on. If the fuel pressuregauge now shows proper fuel pres-sure, you know the fuel pump circuitand pump are functioning properly.

Your diagnostic focus should moveto the command side of the circuit.The PCM may not be receiving thenecessary enabling criteria to activethe fuel pump circuit. This may becaused by a faulty input sensor, low oilpressure or some other factor. Theprocess described above took less thanfive minutes. If you had to manuallytest the fuel pump circuit, it wouldlikely take three times as long.

As another example, a Honda Civicrecently rolled into my shop with themalfunction indicator light (MIL) illumi-nated. I retrieved the DTCs and found a

P1404 (EGR Stuck Closed). At this pointI had to determine if the problem cur-rently existed or if it was an intermittent.

Fig. 2 shows screen captures fromthe Teradyne Pocket Tester. Box 1shows the EGR Test under the Inspec-tion Menu. To the right of the EGRTest is a box circled in red. This is aninformation box; when selected, it willprovide details about the test you’reabout to perform. Box 2 provides criti-cal instructions related to the test. Box3 shows the start of the test process.Box 4 instructs you to increase the en-gine speed to between 2500 and 3000rpm. Box 5 shows a sample of the databeing considered during the test. Thebar graph in the center is for the EGRLift Sensor. Based on the reading, itlooks like the EGR Valve is functioningat this time. Box 6 shows the results ofthe EGR Test. The system is normal at

this time. If you suspect the EGR valvemay be sticking intermittently, youmight want to run this test severaltimes. If the EGR valve test failed asubsequent test, you could proceedwith checking and/or replacing theEGR valve.

I also recently serviced a 1995Dodge Stratus with an illuminatedMIL. The DTC was a P0443 (EvapPurge Solenoid Circuit). The diagnos-tic information shows the DRB IIIfactory scan tool is capable of com-manding the purge solenoid open andclosed. The Vetronix Mastertech andSnap-on Scanner also can perform thistest.

Fig. 3 on page 42 shows screen cap-tures from the Vetronix Mastertech3100. Box 1 shows the F6: Purge Testoption. Box 2 provides the option ofblocking or permitting purge flow. Inthis case, we need to select F1: Flow.Box 3 provides a suggestion: An inspec-tion of vacuum lines and hoses may re-veal a problem. This is an importantnote; many problems can be discoveredquickly with a visual inspection. Box 4explains that the up and down arrowson the scan tool control the purge sole-noid. Box 5 displays the initial LongTerm Adaptive Fuel Trim values forBanks 1 and 2.

Once the purge valve is commandedopen, we expect the fuel trim values tochange based on what’s present in thegas tank. If there’s a high concentrationof fuel vapors present, the fuel trim willdecrease to compensate for the richair/fuel mixture condition. If there’s ahigh concentration of oxygen, the fueltrim will increase to compensate for thelean air/fuel mixture condition. In Box6, the purge valve was commanded on.The upper box shows the initial test: nochange in fuel trim. At this point, I sus-pected a sticking purge solenoid. I cy-cled the purge valve on and off severaltimes and on the third try, the fuel trimlevels increased, indicating the solenoidopened. Based on the results, the purgesolenoid should be replaced.

The next vehicle is a 2004 ToyotaCamry with the SRS and PassengerAir Bag lights illuminated. This vehiclewas sent to us by a body shop, follow-ing accident repairs. A Mastertech

40 April 2005

BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAY

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with Toyota software isneeded to access this system.For most shops, diagnosingand repairing this problemwould not be an option, un-less they have the necessaryequipment. Using the Mas-tertech, I retrieved DTCB1782 (Occupant Classifica-tion Sensor Rear LH CircuitMalfunction). After consult-ing the diagnostic informa-tion, a visual inspection re-vealed the Rear LH sensorconnector was not fully con-nected.

Figs. 4-6 are screen cap-tures taken from the Mastertech. InFig. 4, Box 2 shows the controller op-tions for this vehicle. After properlyconnecting the sensor, we should checkthe sensor data (Box 3). In Box 4, all ofthe sensors are reading, but the sensorweights range from �5.50 to 6.60 lbs.The diagnostic chart recommendedperforming a Zero Calibration after seatreplacement.

Fig. 5 shows the screen captures re-lated to Zero Calibration. Box 1 ZeroCalibration is option 5. Box 2 and Box 3provide specific instructions to preparefor the test. Box 4 indicates that ZeroCalibration is complete and recom-

mends performing a Sensitivity Check.Fig. 6 shows the screen captures re-

lated to the Sensitivity Check. Box 1Sensitivity Check is option 6. Box 2 pro-vides instructions to begin the test. Box3 is the first sensor reading measure-ment. The sensor reading is 0.00 lbs.,which passes the �7 to �7 lbs. test.Box 4 indicates that 66 lbs. of weightneed to be placed on the seat. Box 5shows three weights—50 lbs., 10 lbs.and 5 lbs.—for a total of 65 lbs., placedon the seat. Box 6 shows the sensorreading with the weights applied. Thereading is 66.00 lbs., which agrees withthe weight we applied and falls within

the 59 to 73 lbs. recommend-ed. As you can see, this repairwould not have been possiblewithout the proper equip-ment. In addition to an en-hanced scan tool with bidirec-tional controls and OEM soft-ware, a weight set is neededto properly perform this test.

When BidirectionalControl Won’t WorkThese examples show just afew of the ways that bidirec-tional controls can be used.The scan tools used provid-ed information on how to

prepare for the tests and explained thetest actuation procedures. However,you may run into a situation where abidirectional control will not actuateor stops working without your control.Fig. 7 on page 46 is a combinationscreen capture from EASE Diagnos-tics and Vetronix scan tools that illus-trates this possibility.

The EASE Chrysler Enhanced soft-ware displays information related tobidirectional controls. The Test De-scription box in the upper left-hand cor-ner indicates the purge solenoid will cy-cle on and off approximately every 1.5seconds. The Notes box in the upper

42 April 2005

BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAY

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right-hand corner indicates the solenoidwill timeout after seven minutes.

The white box with blue border inthe lower right corner shows Mas-tertech screen captures from a 1995Dodge Stratus. In red are two boxes la-beled Time On and Time Off. At3:52:59 p.m., I commanded the purgesolenoid on. Approximately 30 secondslater, at 3:53:32 p.m., the solenoidturned off. This automatic-off proce-dure is designed to protect the sole-noid. Depending on the component ortest, the solenoid may turn on again af-ter a specific period of time.

This example demonstrates that theinformation provided to the scan toolmanufacturers is not always accurate. Isthis a significant issue that will preventme from diagnosing this vehicle? No. Ihad a basic understanding of what thetest was going to do and the test per-formed the necessary function: openingand closing the purge solenoid. It wouldbe nice if the information were accu-rate, but in many instances, the infor-mation is released to the scan tool de-signers before the first production vehi-cles have even left the assembly plant.Vehicle engineers can and do makechanges after this point that are not re-flected in the original scan tool designspecification. Also, once vehicles are on

the road, PCM reprogramming canchange bidirectional control specifica-tions and operation in ways that are notreflected in the scan tool information.

There’s a lot more that could be writ-ten about bidirectional controls andtheir place in your diagnostic routine.But how much more? Until recently, Iwasn’t even sure how many bidirection-al functions and tests were available foreach of the current scan tools. To get ageneral idea, I called Bob Augustine atVetronix and asked about the capabili-ties of the Tech 2. As it turns out, GMhas a set of documents called the Tech2 Pathing Tables. These are basicallythree separate documents: Body, Pow-ertrain and Chassis. All together, they’re14 pages long and list more than 1300tests in alphabetical order—1300 tests!If you own a Tech 2, you need thesedocuments, which can be purchasedfrom ACDelco at acdelcotds.com/store.All three sections are sold as a set for$25 under Part No. ROM00190. Simplyinsert the part number into the ItemSearch box and select Search. The doc-ument is displayed with a descriptionand cost. GM also offers a handy pocketreference card, Part No. ROM00164.

Here’s an example of how thePathing Tables can help: A GM vehi-cle equipped with electric mirrors is

43April 2005

Fig. 6

not working properly. You’d like totest the operation of the Driver’sElectric Mirror using the Tech 2, butdon’t know where to find the specific

tests. Using the Body Pathing Table,simply look up Driver’s Electric Mir-ror in the alphabetical chart. Driver’selectric mirror functions are located in:

Body-Memory Mirror Module-SpecialFunctions-Output Controls. Fromhere you can command the mirrorDown/Left/Right/Up.

Among the other function tests Ifound interesting are IncandescentDimming, Microphone Test, Military orStandard Time, Phone Call Test/OnStarand Theater Dimming. This is just onevehicle manufacturer and one factoryscan tool. Multiply this by 22 vehiclemanufacturers and you can see thatthe scan tool’s potential power is in-credible.

Can you afford to work only on old-er vehicles and limit yourself to justengine control systems? Maybe, butfor how much longer? My advice is toget ready to invest a lot more money inscan tools. The benefits will far out-weigh the cost in the long run.

46 April 2005

BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAY

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