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Internal Electronic Component TestingThe Input Speed Sensor (ISS) (2 wire Hall effect) is located on the rear cover with theharness routed inside to the TECHM.The Output Speed Sensor (OSS) (2 wire Hall effect) are located underneath the valve bodyand TECHM as shown here.Output Speed Sensor (OSS)Be Careful Not ToPinch This WireUnder The Valve BodyInput Speed Sensor (ISS)

Internal Electronic Component TestingThe Output Speed Sensorsignal is generated by therotation of the park gear.3-5-R ClutchAssemblyInput SpeedSensorPark GearInput Speed Sensor signals aregenerated by the rotation of the3-5-R clutch assemblies and areused to calculate gear ratio andslip rates.

Internal Electronic Component TestingThere are some external electronic tests that can be performed before the transmissionis removed. A harness off an old speed sensor would be a great tool for this.The speed sensors can be unplugged and a sensor simulator can provide a signal to theTECHM while the information can be monitored on scan tool data.Then it can be verified if the TECHM can read the signal.Re-connect External Harness HereSensor Simulator

Internal Electronic Component TestingThis process can also be performed on the bench as well with a Kent Moore DT48616-10adapter cable.DT48616-10Tech IISolenoid cleaning procedure has beenremoved from the GM Tech2 in 2009Sensor Simulator

Internal Electronic Component TestingThe 6T40/6T45 Internal Mode Switch is connected mechanically to the manual shaft similarto the 4T65E application.Electrically the IMS operates similar to other GM IMS applications. The TCM sends a biasvoltage to the IMS on 4 circuits, A, B, C, P. Pin N is used for Park/Neutral startingoperations and is supplied by the ECM. As the range selector is moved the IMS willground/unground the circuits or circuit required to indicate the specific manual valveposition.By monitoring the voltage sequence produced,the TCM will be able to identify the range thatwas selected.

Internal Electronic Component TestingThe IMS can also be tested while still in the vehicle.With the IMS disconnected jump ground the pins on the TECHM while monitoring the scantool data with the key on engine off (KOEO). The external case harness has to beconnected.Re-connect ExternalHarness HereDisconnect IMSIMS Harness Connector

Internal Electronic Component TestingSimultaneously supply a ground to the IMS pins in the TECHM and check the chart withscan tool data to confirm proper operation.A GroundB Mode Switch Signal “P”C Mode Switch Signal “C”D Mode Switch Signal “B”E Mode Switch Signal “A”F P/N Start Signal “N” to ECMTECHM IMS PinsA harness cut from an old IMS wouldwork great for doing this test.

Internal Electronic Component TestingOne important test often overlooked during diagnosing a 6T40 with solenoid functionalcodes present not electrical.An automated process is available that aids in cleaning debris from the solenoid assembly.A capable scan tool will instruct the TCM (TEHCM) to cycle the solenoids while the systemis pressurized to clean the solenoids. The transmission does not need to be disassembledto perform the cleaning process.Simply follow the instructions on the scan tool to activate the cleaning program. Thisprocess should be completed prior to attempting to diagnose the transmission. If thecleaning process is unsuccessful then you should diagnose the concern with Kent MooreDT47825 tool kit.

Internal Electronic Component TestingThis process can also be performed on the bench as well with the Kent Moore DT47825test tool kit and scan tool.Kent Moore DT47825DT 48616Kent Moore DT48616-10Tech II Adapter Cable

Internal Electronic Component TestingRemove the Control Solenoid Valve Assembly from the transmission. Install tool DT 48616onto the Control Solenoid Valve Assembly (5Nm 44 Lb In). Apply regulated shop air (90-100psi) to the tool. Connect the scan tool to the Control Solenoid Valve Assembly using cableDT48616-10.Command the solenoid ON/OFF air pressure should be present on the gauge and then itshould exhaust as the solenoid is cycled. If the solenoid or valve are malfunctioning thegauge pressure will not change as you cycle the solenoid. If a malfunction is determined tobe present, replace the complete Control Solenoid Valve Assembly.If the solenoid checked OK, install the gauge on another solenoid port and command thatsolenoid ON/OFF with the scan to repeat the process.

Internal Electronic Component TestingNOTE: The TCM (TEHCM) will normally cycle several of the solenoids ON/OFF to help keepthe solenoids and the valves free of debris.Therefore this cleaning function (Dither) may cause the gauge to flicker when the TCM iscleaning the solenoid you are testing.Do not operated the solenoids for longer than 2 minutes or damage may occur.DT 48616GaugeTech IIDT 48616BoltsGaugeDT48616-10DT48616-10

False Solenoid Performance CodesThere may be times when there is a solenoid performance code is caused by a problem withthe pressure switches found on the GEN I models. Eliminated on GEN II models in 2012.Any solenoid performance code found on any models vehicle can be caused by any type ofpressure leak in the clutch circuit controlled by the solenoid in question.In this case the code was caused by a leak in the pressure switch circuit by a failed solenoidgasket.The code can also be caused by a failed TECHM.TornGEN IIThe early gasket will work on allGEN I, II & III models.

False Solenoid Performance CodesThere are repair kits available in the aftermarket for the GEN I pressure switches.The pressure switches were eliminated in 2012 because of an excessive failure rate.One issue is the pressure switch retaining rivets become loose.When repair existing pressure switches always check for loose rivets.Replace switches (part of the TECHM) when necessary.GEN ILoose RivetsDamagedDamaged

Solenoid InformationUnlike the Ford version of this transmission (6F35) or the GM 6T70 series, these solenoidscan be removed. The solenoids can be checked or moved as a test to another location withthe same connector color (normally high or low).R1-4-5-6Clutch#3 N/H1-2-3-4Clutch#5 N/HShiftTCCSolenoidPressure on/offControl(N/C)N/L3-5-RClutch#2 N/L2-6Clutch#4 N/LRemove RetainerLinePressureN/HGEN IINo Pressure Switches(missing screens)Available separately from the aftermarket

No Forward Reverse OkWhen this symptom arrives at your shop and the IMS and solenoid signal (command) datalooks fine on the scan tool. After checking all the power and grounds to the transmission,the only choice we have is to replace the TECHM.Well, one did come in with this symptom and the (#5) 1-2-3-4 Clutch Pressure Controlsolenoid (N/L) was swapped with the (#4) 2-6 Clutch Pressure Control solenoid (N/L).The vehicle then had forward butno 2nd or 6th gear.R1-4-5-6Clutch#3 N/H3-5-RClutch#2 2-3-4Clutch#5 N/LWith this simple test the end resultwas to replace the 1-2-3-4 PC Sol.#5.Saving time and money on anew TECHM.Note: connector color is just forfactory identification of solenoidsupplier that made the solenoid forGeneral Motors.Replacement solenoid connectorcolor may be different.GEN IPressure Switches(all screens)2-6Clutch#4 N/LLinePressureN/H

DTCs Set After TEHCM ReplacementAfter swapping TEHCMs from another application or installing a new or reman TEHCM youmay have a DTC P0713/ P06AE set.The transmission may exhibit numerous other symptoms such as transmissiontemperature reading -25 to -40 and major operational issues as the 1-2-3-4 and 3-5-Rsolenoids have changed position from GEN 1 to GEN 2/GEN 3 (shown previously).Gen 1 and Gen 2 transmissions use the same RPO codes.The generation of transmission can be determined by inspecting the parts/components (Nopressure switches on GEN 2, or by looking at positon #8 of the bar code number stampingon the TCM, Number GEN 1, Letter GEN 2)It can also be determined by using a scan tool whilethe transmission is still in the vehicle.Using your scan tool see if DTC P0842 or any of theother pressure switch DTCs that were previouslyused are listed as a valid or invalid code.If pressure switch DTCs display as valid, thetransmission is a Gen 1. If DTC shows invalid, thetransmission is a Gen 2 or GEN 3.GEN II

DTCs Set After TEHCM ReplacementGEN I & GEN II TECHM can be Identified by the 8th digit on the cover. If it’s a letter it’s aGEN I a number it’s a GEN II.GEN ITemperature Sensor

Valve Body ProblemsThe 3 most common valve or valve bore wear areas are (most transmissions):1: Actuator Feed Limit2: TCC Regulator3: Line Pressure (next page)In that order.Note:GEN I valve bodyonly has 10 valves,1 valve is locatedin different positionwhile another valvehas changed onGEN 2 models.Always check all valves and bores for wear.GEN IIManual Valve(not found in GEN I)R1/4-5-6 Clutch Boost (located here)#1 Actuator Feed LimitR1/4-5-6 Clutch RegulatorClutch Select(No Valve Located Here GEN I)1-2-3-4 Clutch Boost1-2-3-4 Clutch Regulator#2 TCC Regulator Apply2-6 Clutch RegulatorHydraulics changein 2012 GEN 2.Default3-5 Reverse Clutch(GEN I Compensator Feed Regulator)

Valve Body ProblemsInspect valvesand borescarefully for anydamage or wearGEN I & IIGEN III Off AxisChain Driven(similar to 6T70)TCC BlowOff BallTCC Control#3 Pressure Regulator(Line)Pump(Line Pressure)Blow Off Ball

False Solenoid Performance CodesA code P2723 Pressure Control Solenoid #5 fault can be caused by a crack found on 1-23-4 clutch bonded (molded) apply piston.Closely look at the piston for any cracks or defects.These bonded pistons should be changed during overhaul.1-2-3-4 Clutch Apply PistonLocated On This Side(bonded)Low/Reverse Clutch ApplyPiston Located On This Side(bonded)

Falling Out Of Gear At A StopA vehicle may arrive at your shop with this complaint hot and/or cold.Check the 1-2-3-4 molded (bonded) apply piston seal, it may have shrunk (new or original).If so there will be no resistance; the piston may just fall into or out of the housing.1-2-3-4 Clutch / L-R Housing1-2-3-4 Clutch Apply Piston(Bonded)Falls Out

Hybrid (RPO KL9) Start/Stop Feature No Longer OperatesAfter Repairs, No Codes SetSeveral different GM applications including the Chevrolet Cruz, Malibu, Cadillac ATS, CTS,CT6, XT5, GMC Acadia and the Buick Encore and Envision may be equipped with a“Hybrid” transmission as well as “Hybrid engine/electrical systems.On these applications the Battery Sensor Module may lose its memory which disables theStart/Stop feature.Start / Stop Feature#2 BAS HybridPump(top of caseabove differential)

Hybrid (RPO KL9) Start/Stop Feature No Longer OperatesAfter Repairs, No Codes SetThe battery sensor module will need to be relearned for the transmission/vehiclestart/stop function to operate correctly.To relearn the battery sensor module you can: Use a scan tool to relearn the values. Leave the vehicle set for a minimum of 3 hours after the modules on the vehicle havegone to sleep.This process triggers the battery sensor module to relearn its values.

Axle Seal LeaksBoth the GM 6T40 and Ford 6F35 series transmissions have chronic complaints of driver’sside axle seal leaks. This is due to an inadequate amount of surface area to support theaxle.This is caused by a worn axle bushing in the case.This would normally require the entire transmission to be disassembled to replace thebushings.There are aftermarket tool kitsto perform the repair withoutremoving the transmission.These kits supply a widerTeflon coated bushing formore support and durability.The bushing also has a lubecutout for better lubrication.Driver’s SideAxle Seal

AWD Final Drive Failure6T40-6T45-6T50 AWD applications may experience a failure of the final drive gear set andbearings.Cause/Correction: This concern is typically due to the bolts breaking that are used to attachthe final drive components, leading to a catastrophic failure of the final drive and itsbearings.When installing the bolts in the final drive componentsyou may want to consider upgrading them to a highertensile strength and the bolts should be properlytorqued and retained with Loctite.Torque & Loctite Bolts

Line Pressure TestTo check line pressure connect a suitable pressure gauge or transducer to the pressure tapindicated in the illustration found on the next page.Remove the line pressure test hole plug (tap) and install a pressure gauge.1. Access the Scan Tool Transmission Output Controls for the Line PC Solenoid.2. Start the engine.3. Note: In order to achieve accurate line pressure readings, the following procedure mustbe performed at least 3 times in order to gather uniform pressure readings. The scan tool isonly able to control the line PC solenoid in PARK and NEUTRAL with engine speeds below1500 RPM. This protects the clutches from extreme high or low line pressures.4. Use the scan tool to increase and decrease the Line PC Solenoid in increments ofapproximately 200 kPa (29 psi). The scan toolcommands the increment values automatically.5. Allow the pressure to stabilize betweenincrements.6. Compare the pressure readings on the J 21867:pressure gauge to the actual pressure values inthe solenoid valve pressure chart. Refer toSolenoid Valve Pressure.

Line Pressure TestThe line pressure data on the scan tool will read in kPA.The chart below will show the pressure converted to psi.Line Pressure Tap

Overheat When Overfilled, Setting Code P0218Overfilling will cause the transmission to overheat and set code P0218 Transmission FluidOver Temperature.The 6T40/45 utilize a thermal type element to control the oil level in the unit similar to otherGM units. Known as a “Fluid Level Control Valve” the unit is basically a thermallycontrolled stand pipe.Fluid Level Control Valve is attachedto the transmission case, next to thecontrol valve body assembly, and isdesigned to control the fluid level inthe control valve body cover assembly.The fluid level control valve contains atemperature sensitive strip of metal thatreacts to fluid temperature changes andopens or closes a fluid passage.The maximum fluid level in the controlvalve body cover area is controlled asfluid overflows the top of the fluidlevel control valve pipe and drainsinto the case sump.Fluid LevelControl Valve

Overheat When Overfilled, Setting Code P0218At temperatures below 60 C (140 F), the thermostatic element allows fluid to drain from thecontrol valve body cover area into the case sump.As the temperature of the transmission fluid increases, the thermostatic element traps fluidin the control valve body cover area and the fluid level rises.This level of transmission fluid is required in order tomaintain the operation of the hydraulic system in thetransmission.Cold OpenA damaged or loose thermostatic element could causefluid foaming or incorrect fluid level.The fluid temperature must be at operating temperature inorder to obtain a proper fluid level in the case.Checking the fluid level with the fluid temperature belowoperating temperature will result in a high fluid level(over filled).This will cause the transaxle to over heat setting code P0218and possibly fluid leaking out of the vent.Warm Closed

Overheat When Overfilled, Setting Code P0218It may be easier to fill to the correct level using the Fluid Capacity chart shown below.If you are changing fluid in these units make sure the unit is cold. If you remove the drainplug in the bottom of the case while still warm only about 50% of the fluid in the unit willdrain.Fluid temp can be checked from the “driver information center” (some models) or by usinga scan tool. It is critical that the fluid be at the correct temperature or an overfill or under fillcondition may occur.These units are easily overfilled because the synthetic fluid’s expansion rate is verysensitive to temperature giving false level readings.As little as ½ qt overfull can lead to fluid leaking from the vent. Fluid level is checked withthe engine running, fluid temp 85 C-95 C (185 F-203 F), in park, via a plug near the axleseal area in the case.Drain Plug

Overheat When Overfilled, Setting Code P0218Take special care when filling these transaxles with fluid.The DEX6 synthetic fluid expansion rate is very sensitive to temperature.Keep in mind that the main transmission filter is internal to the unit, located in the sump.As you can see the case would have to be separated to service this filter.Fill PlugOil Level Set PlugMain Filter in Sump

Overheat When Overfilled, Setting Code P0218Fluid temp can be checked from the “driver information center” (some models).If equipped the procedure can be found in the owners manual.

No Movement After ReflashWhen reflashing some GM vehicles with an aftermarket scan tool the transmission will notengage. It may remain in neutral until the scan tool is removed.Note: This has also been known to happen on other GM 6 speed units as well.The actual reprogramming procedure for a GM vehicle goes as follows:1. Check the calibration history of the vehicle. Go to the GM web page athttps://tis2web.service.gm.com/tis2web and see what latest program is for the vehicleusing the vehicle’s VIN number. If the programming has been updated to correct aproblem, it will be listed on the website2. Connect your PC to the Tech 2 scan tool (or aftermarket scan tool/laptop software) with aRS232 cable pass-thru device.3. Start the GM recalibration software program on your PC and enter the vehicle applicationinformation (year, make, model, etc.).4. Connect the Tech 2 scan tool to the diagnostic connector on the vehicle (located underthe dash near the steering column).5. Switch the Tech 2 scan tool on and wait for the Start Screen.6. Validate the vehicle VIN number.7. Choose the operating system, engine, fuel system, speedometer or transmission.

No Movement After Reflash8. Select “normal reprogramming” or “VCI” (special modifications).9. Choose the update bulletin/recalibration number from the menu.10. Start the transfer of data. The reprogramming procedure takes about three minutes, andcan be done with the computer in or out of the vehicle. The PC screen will display a blueprogress bar as the software is uploading to the vehicle.Note: The GM setup will not allow the same calibration to be reinstalled over itself. Only anupdated calibration can be loaded into the vehicle computer.11. When the software has finished loading, themessage “PROGRAMMING COMPLETE” willappear. But there is no message to disconnectthe scan tool and when left connected thetransmission will remain in neutral.12. The scan tool can now be disconnected fromthe vehicle (turn ignition off first), and anysubsequent relearning procedures that may beneeded such as the crankshaft position variationrelearn procedure can now be performed to finishthe update.

Transmission Adaptive Values LearnTransmission Adaptive Values Learn is a procedure for 6 speed automatic transmissionsin which a series of tests are run to allow the transmission control module (TCM) to learn

1 Code for Automatic Transmission 2 Model Year 3 Model for Transmission 4 Transmission Family 5 Source Code for Plant 6 Calendar Year 7 Julian Date 8 Shift/Line (A/B) 9 Numeric sequence starting at 0001 @ 12:01 AM each day There will be times when a v