Bench Testing The 6L50-6L80-6L90-6T70-6T75 TEHCM Bench

Bench Testing Bench Testing the 6L50-6L80-6L90-6T70-6T75 TEHCMXLI 0 0 0 8 8 8),'1by Steve Garrettmembers.atra.comwww.atra.comFigure 1In past articles, I’ve spent a lotof time covering the operationof GM’s solenoid body/controller, better known as a TEHCM(Transmission Electrical HydraulicControl Module)The TEHCM houses the TCM,shift solenoids, PWM solenoids, pressure switches, and temperature sensorsfor the transmission or transaxle. It’smounted inside the unit, attached tothe valve body. The TEHCM communicates with the components outsidethe transmission or transaxle via the14data bus.Testing the components requiressome special tools, including:% Scan tool% DT47825-100 solenoid test plate% Appropriate vehicle interfaceharness DT47825-20 (6T706T75) or DT47825-10 (6L506L80-6L90)% DVOM% Signal generator, such as KentMoore J-38522 (EL38522)Many technicians inquire regarding the procedure to bench test theTEHCM. GM developed a test plateto allow you to conduct static tests ofthe solenoids. A static test will helpyou find a solenoid that’s stuck open orclosed, but it won’t show you whethersolenoid flow rate is correct at variouscommanded positions.You can use the test plate anytimeyou have the TEHCM removed fromthe vehicle, such as during a rebuild.You’ll need the vehicle to complete thistest, because the scan tool still relies onthe vehicle data bus for communicationwith the TEHCM.GEARS August 2012

Bench Testing the 6L50-6L80-6L90-6T70-6T75 TEHCMFigure 2AFigure 2BThe process is the same for bothRWD and FWD 6-speed applications,although the harness interface partnumbers will vary with the application.To bench test the TEHCM:% Remove the TEHCM from thetransmission or transaxle.% Attach the DT47825 test blockto the TEHCM using the boltssupplied with the tool. Torquethe bolts to 44 lb-in (5 Nm)working from the center out.% Install the pressure gauge supplied with the tool to the solenoid you want to test.% Connect the appropriate interfaceharness between the TEHCMand the vehicle harness.% Key on, engine off.16% Connect your scan tool to thevehicle, and select output overrides to allow you to cycle thesolenoids on and off with yourscan tool.% Attach shop air to the DT47825test block; adjust to 90-100 PSI(figure 1).% Cycle the solenoid on and offwith your scan tool while monitoring the gauge on the testblock.When you’re done testing a solenoid, simply move the pressure gaugeto another port on the test block andrepeat the procedure until you’ve testedeach solenoid multiple times.Note: A solenoid timeout featurewill prevent you from operating thesolenoids too long. This is designed toprevent damage to the TEHCM.Refer to the GM diagnostic chartsto determine when the gauge shouldread or not read pressure (figures 2aand 2b). If the TEHCM fails to operateas indicated, you’ll need to clean orreplace the TEHCM.NOTE: With the key on, engineoff, the TEHCM will normally cyclesome of the solenoids on and off; thisis part of the software program. Thismeans you may appear to have air flowfrom some of the test plate ports priorconducting the test. This is normal andit’s part of the solenoid cleaning program that the TEHCM conducts.GEARS August 2012

Bench Testing the 6L50-6L80-6L90-6T70-6T75 TEHCMGM limits bench diagnosis of thesolenoids to using the test plate. Butyou can test solenoid electrical operation with a DVOM, just as you wouldany other solenoid.Lay the TEHCM on the bench andinspect the solenoid terminals on theside of the TEHCM for any debris thatmay be bridging the terminal welds. Ifyou discover any debris, clean it off; itmay be causing the problem.If no debris is present, set yourmeter to measure Ohms and connectthe leads across the solenoid you wishto test. The solenoid resistance shouldread:Shift Solenoid (On/Off solenoid)20-40 ohms (figure 3A).Shift and Line Pressure Solenoid(PWM solenoid) 3-8 ohms (figure 3B).You can also check current flowthrough the solenoids. The manufacturer doesn’t recommend this test forPWM solenoids, but it can be done in asafe manner if you limit how long youleave the current flowing through thesolenoid.% Connect one solenoid terminal toa fused voltage supply.% Using your meter, connect theother solenoid terminal to thevoltage supply ground; don’tleave the solenoid energized toolong.% Read the amperage on yourmeter. Normal amperage basedat normal solenoid resistancesand a measured 12-volt supplyshould be:Shift Solenoid (On/Off solenoid) 0.3–0.7 amps at 12 volts(figure 4A).Shift Solenoid (PWM solenoid) 1.5–4.0 amps at 12 volts(figure 4B).If the resistance or the amperagevalues are incorrect the solenoid hasfailed and you’ll need to replace theTEHCM.Figure 3A: On/off Solenoid resistance: 20-40 ohmsSolenoid CleaningProcessIf you have a solenoid performance DTC or the solenoid fails theair bench test, you should try the solenoid automated cleaning process beforereplacing the TEHCM. This processtakes place when the TEHCM is in thetransmission and the transmission is in18Figure 3B: PWM solenoid resistance: 3-8 ohmsthe car.Solenoid cleaning is an automatedprocess initiated by your scan tool. Ifyour scan tool is equipped, the processwill raise engine RPM and raise andlower line pressure while the solenoids are being commanded on andoff by the TCM. This process is fullyGEARS August 2012

Bench Testing the 6L50-6L80-6L90-6T70-6T75 TEHCMautomated so once the vehicle is in parkand you’ve selected the feature on thescan tool, it’ll cycle all of the solenoids,flushing debris from the solenoids andtheir circuits.If the performance DTC resets orthe bench test fails, you’ll need toreplace the TEHCM. If the problemsappear to be gone after the cleaning,you can reuse the TEHCM.TEHCM Speed SensorTestingYou can test the speed sensors inthese transmissions and transaxles bysupplying a substitute signal to isolatewhether the problem is in the sensor orthe TEHCM. The sensors feed their signals directly into the TEHCM. A signalgenerator can simulate the signal fromthe sensors.% Connect your signal generator tothe speed sensor wiring connector on the TEHCM.% With your scan tool connected tothe vehicle, monitor the ISS andOSS signals on the scan tool.The signal generator creates an8-volt square wave and can vary thefrequency of the signal. As you changethe frequency, the speed indicated onthe scan tool should change with it.If the scan tool speed sensor signalchanges as you vary the frequency onthe signal generator, the TEHCM isworking properly, so the problem isprobably the speed sensor itself. If thespeed signal isn’t present on the scantool, the problem is likely the TEHCM.Figure 4A: On/off Solenoid amperage: 0.3-0.7 ampsReplacing the TEHCMIf your diagnosis has led you toreplace the TEHCM, there are a fewthings you should keep in mind:% The TEHCM will require programming to match the vehicleor it won’t operate.% You’ll need to perform a FastLearn procedure to establish thebaseline shift adapt values orshift problems will occur.% You’ll need to replace the filterplate; never try to reuse the filterplate.That’s about it for now, so untilnext time, remember: “Our aspirationsare our possibilities.”Figure 4B: PWM solenoid amperage: 1.5-4.0 amps20GEARS August 2012

New Transmission-by-Vehicle Appfor smart phonesNew, Global EditionTransmission AppSimplifies IdentifyingTransmissions by VehicleYou can now use your mobile phone to identify automatictransmissions in virtually any vehicle in the world.tranDevDevelopedto eliminate confusion over look-alike transmissions,this mobile app identifies transmissions by vehicle make, model,year and engine for import and domestic applications throughthe 2012 model year and is updated continuously with newvehicle listings.You can select Honda, for example, to learn that a 2002 HondaAccord with V6 3.0L engine has a 4-speed, front wheel drivetransmission (model B7XA).K[Yf oal qgmj keYjl h gf] Yf\ ZggceYjc 4 s & s -ILAN /(A Division of Freudenberg-NOK Sealing Technologies

each solenoid multiple times. Note: A solenoid timeout feature will prevent you from operating the solenoids too long. This is designed to prevent damage to the TEHCM. Refer to the GM diagnostic charts to determine when the gauge should read or not read pressure (figures 2a and 2b). If th