GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Yukon Denali 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E/4L85-E 🢒 DTC P0742

Object Number: 525796 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The transmission control module (TCM) energizes the torque converter clutch pulse width modulated (TCC PWM) solenoid valve by grounding the control circuit. This blocks the exhaust for TCC signal fluid and allows filtered 2-3 drive fluid to feed the TCC signal circuit. When the vehicle operating conditions are appropriate for TCC application, the TCM increases the TCC duty cycle to approximately 30 percent. This allows TCC signal fluid pressure to move the converter clutch shift valve into the apply position and direct regulated apply fluid to the torque converter. The TCM then increases the duty cycle to approximately 60 percent, where regulated apply fluid pressure, applies the converter clutch. The vehicle application determines the TCC apply rate. Once the TCC applies, the duty cycle immediately increases to approximately 70 percent to achieve full apply pressure, in the regulated apply fluid circuit.

The TCC PWM solenoid valve is de-energized by the TCM opening the control circuit. This action allows the TCC signal fluid to exhaust through the solenoid and blocks filtered 2-3 drive fluid from entering the TCC signal circuit. The loss of fluid pressure in the TCC signal circuit releases the TCC.

If the TCM detects low TCC slip when the TCC is commanded OFF, then DTC P0742 sets. DTC P0742 is a type B DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0742 Torque Converter Clutch (TCC) System - Stuck On

Conditions for Running the DTC
    • No AT ISS DTCs P0716 or P0717.
    • No OSS DTCs P0722 or P0723.
    • No TCC DTC P0741.
    • No TCC electrical DTC P2763 or P2764.
    • The system voltage is 8-18 volts.
    • The engine run time is 5 seconds or greater.
    • The gear ratio is between 0.95:1 and 1.56:1.
    • The engine torque is greater than 50 N·m (37 lb ft).
    • The transmission fluid temperature (TFT) is between 20°C and 130°C (68°F and 266°F).
    • The commanded gear is not 1st.
    • The calc. throttle position is 8 percent or greater.
    • The vehicle speed is greater than 16 km/h (10 mph).
    • The TCC is commanded OFF.

Conditions for Setting the DTC

The TCC slip speed is between -15 and +15 RPM for 6 seconds or greater 4 times during the same ignition cycle.

Action Taken When the DTC Sets
    • The TCM requests the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
    • The TCM commands maximum line pressure.
    • The TCM forces the TCC ON.
    • The TCM freezes transmission adaptive functions.
    • The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records.
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records.
    • The TCM stores the DTC P0742 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC
    • The ECM turns OFF the MIL during the third consecutive trip in which the TCM does not send a MIL illumination request.
    • A scan tool can clear the MIL/DTC.
    • The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
    • The TCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the TCM.

Diagnostic Aids
    • If the TCC is mechanically stuck ON with the parking brake applied and any gear range selected, the TCC fluid mechanically applies the TCC. TCC fluid mechanically applying the TCC can cause an engine stall.
    • A stuck TP sensor may set a DTC P0742.
    • DTC P0742 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step verifies that the PCM commanded the TCC PWM solenoid valve OFF and the slip speed is -15 to +15 RPM.

Step

Action

Value

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: 

       • Before clearing the DTC, use the scan tool in order to record the ECM Freeze Frame and the TCM Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the ECM and TCM.
       • Using the Clear Info function erases stored DTCs in both ECM and TCM.

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Select TCC Duty Cycle and TCC Slip Speed on the scan tool.
  6. Drive the vehicle in D4 with the calc. throttle position greater than 8%. Allow the transmission shift to 4th gear.

While the TCC duty cycle is 0%, does the scan tool display a TCC slip speed within the specified range?

-15 to +15 RPM

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3
  1. Inspect the transmission for the following conditions:
    2. • The TCC PWM solenoid valve is stuck ON
    • Converter clutch apply valve stuck in the apply position
    • Restricted apply or release passage
    • Valve body gasket for misalignment or damage
    • Restricted transmission cooler line
    • Torque converter mechanically stuck ON
  2. Repair any of the above conditions as necessary.

Did you complete the repair?

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Go to Step 4

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4

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
    4. • Operate the vehicle in D4 with the TCC duty cycle 0% and throttle above 8%.
    • Ensure that the TCC slip speed is between 100 RPM and 1500 RPM for 5 seconds or greater.
  4. Select Specific DTC.
  5. Enter DTC P0742.

Has the test run and passed?

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Go to Step 5

Go to Step 2

5

With the scan tool, observe the stored information, capture info and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

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Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK