GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Chevy MD Steel Tilt (W Model) 🢒 DTC 🢒 DTC P0742 TCC System Stuck On

Object Number: 69046 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics Diesel
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Vehicle Control Module (VCM) energizes the Torque Converter Clutch Pulse Width Modulated Solenoid Valve (TCC PWM Sol. Valve) by grounding circuit 418. This blocks the exhaust for TCC signal fluid and allows filtered 2-3 drive fluid to feed the TCC signal circuit. When the vehicle's operating conditions are appropriate for TCC application, the VCM begins the TCC duty cycle to approximately 30%. 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 VCM then increases (ramps) the duty cycle to approximately 60%, 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% to achieve full apply pressure, in the regulated apply fluid circuit.

The TCC PWM Sol. Valve is de-energized by the VCM opening circuit 418. 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 VCM detects low TCC slip when the TCC is commanded OFF, then DTC P0742 sets. DTC P0742 is a type D DTC. For California emissions vehicles DTC P0742 is a type B DTC.

Conditions for Setting the DTC
    • No Manifold Absolute Air (MAP) Sensor DTCs P0106, P0107, or P0108.
    • No Throttle Position (TP) Sensor DTCs P0121, P0122 or P0123.
    • No OSS DTCs P0502 or P0503.
    • No A/T ISS Sensor DTCs P0716 or P0717.
    • No TCC DTCs P0741 or P1860.
    • No TFP Valve Position Sw. DTC P1810.
    • Engine speed is 900-4700 RPM.
    • The engine torque must be 75-500 N·m (60-400 lb ft).
    • No TFP Val. Position Sw. change within 5.0 seconds.
    • The TFP Val. Position Sw. must indicate D4, for at least 10 seconds.
    • The commanded gear must be 2nd, 3rd, or 4th.
    • Engine speed is 900-4700 RPM.
    • The Throttle Position is 12%.-100%.
    • Vehicle speed is 7-75 MPH.
    • The TCC slip speed must be -10 to +10 RPM for at least 4.0 seconds.
    • All conditions met for 7 occurrences.

Action Taken When the DTC Sets
    • The VCM illuminates the Malfunction Indicator Lamp (MIL) for California emissions vehicles.
    • The VCM commands maximum line pressure.
    • The VCM freezes shift adapts.
    • DTC P0742 is stored in VCM history.

Conditions for Clearing the DTC
    • The VCM turns OFF the MIL after three consecutive trips without a failure reported.
    • A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported.
    • The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

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.
    • First diagnose and clear any engine DTCs or TP Sensor codes that are present. Then inspect for any transmission DTCs that may have reset.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests the mechanical state of the TCC. When the VCM commands the TCC solenoid OFF, the slip speed should increase.

P0742

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Install the Scan Tool .
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the stored Freeze Frame and/or the Failure Records from the VCM.

  3. Record the DTC Freeze Frame and Failure Records.
  4. Select Scan Tool TP Angle and TP Sensor.
  5. Apply the accelerator pedal.

Are the TP Sensor values within the specified range?

0.2-0.9 volts at 0% to 4.5 volts at 100%

Go to Step 3

Go to Diagnostic Aids

3

Drive the vehicle in the D4 drive range in fourth gear under steady acceleration with a TP Sensor angle greater than 12%.

Does the scan tool display a TCC Slip Speed of -10 to +10 RPM while the displayed TCC Duty Cycle is 0%?

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Go to Step 4

Go to Diagnostic Aids

4

The TCC is mechanically stuck ON.

Perform the following inspections:

  1. Inspect the exhaust orifice in the TCC PWM Sol. Valve for any clogging.
  2. Inspect the converter clutch apply valve for the possibility of being stuck in the apply position.
  3. Inspect the valve body gasket for misalignment or damage.
  4. Inspect for a restricted release or apply passage.
  5. Inspect for restricted transmission cooler line.
  6. Refer to Torque Converter Clutch Stuck On .

Did you find and correct the condition?

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Go to Step 5

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5

In order to verify your repair, perform the following procedure:

  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 12%.
    • Ensure that the TCC slip speed is greater than 175 RPM for 6 seconds.
  4. Select Specific DTC. Enter DTC P0742.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1