Circuit Description
The Transmission Control Module (TCM) controls the Torque Converter Clutch (TCC) solenoid valve Pulse Width Modulation (PWM). The solenoid directs the hydraulic fluid for TCC apply and release. When the TCC is released, the engine is coupled by fluid to the transmission and TCC slip speeds of -300 to +1,500 RPM during heavy acceleration.
If the TCM detects a low torque converter slip when the TCC is commanded off, then DTC P0742 sets, which is a type 'B' DTC.
Conditions for Running the DTC
| • | Ignition voltage is between 8.0 and 18.0 volts. |
| • | Engine speed is between 450 to 6,800 RPM for at least 5 seconds. |
| • | No engine torque defaults are current. |
| • | The following DTCs are not set: |
| - | P0121, P0122 or P01230--Throttle Position Signal |
| - | P0716 or P0717--Transmission Input Speed Sensor |
| - | P0722 or P0723--Transmission Output Speed Sensor |
| - | P0741--TCC System Stuck OFF |
| - | P0815, P1820, P1822, P1823, P1825 or P1826 - Transmission Manual Shift Shaft Switch Assembly |
| - | P02637-- Engine Torque Signal Circuit - No Valid GMLAN Signal |
| - | P02763 or P02764--TCC Solenoid |
| • | The transmission is not in 1st gear and the gear ratio is 0.73:1 to 2.27:1. |
| • | The transmission fluid temperature is between 20 to 130°C. |
| • | The transmission manual shift shaft switch assembly is D5 range. |
| • | The engine torque is between 80 and 450 N·m. |
| • | The engine speed is greater than 500 RPM. |
| • | The throttle position is 15-90%. |
| • | The TCC is commanded OFF. |
| • | The vehicle speed is greater than 15 km/h. |
Conditions for Setting the DTC
The following condition occurs more than three times in the one ignition cycle:
The TCC slip is between -20 to +20 RPM for a time period of greater than 3.5 seconds.
Action Taken When the DTC Sets
| • | The TCM requests the ECM to illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the 'Conditions for Setting the DTC' have been met. |
| • | At the time of the first failure, the TCM records the operating conditions when the 'Conditions for Setting the DTC' have been met. The TCM stores this information as a Failure Record. |
| • | At the time of the second failure, the ECM records the operating conditions when the 'Conditions for Setting the DTC' are met. The ECM stores this information as a Freeze Frame. |
| • | The TCM freezes the transmission adaptive learning function. |
| • | The TCM stores DTC P0742 into TCM history. |
Conditions for Clearing the MIL/DTC
| • | Tech 2 can clear the DTC. |
| • | The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring. |
| • | The TCM cancels the default actions when the ignition is off long enough to power down the TCM. |
| • | The TCM turns off the MIL after the sixth consecutive drive trip in which the TCM does not send an MIL illumination request. |
Diagnostic Aids
Rapid fluctuations in line pressure may set DTC P0742.
The customer may notice an engine stalling condition.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
2. This step inspects the transmission fluid to ensure that it is at the proper level.
3. This step verifies that the TCC engages when commanded on by Tech 2.
4. & 5. Checks for a short to ground or open circuit in the solenoid supply circuit.
6. Checks for short to voltage on the solenoid supply circuit.
7. Checks for short to ground on the solenoid supply circuit.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics For information on testing wiring faults, refer to Wiring Systems. | ||||||||||||
1 | Has the Diagnostic System Check - Automatic Transmission been completed? | -- | Go to Step 2 | |||||||||
2 | Perform the transmission fluid checking procedure. Refer to Transmission Fluid Check Did you perform the fluid checking procedure and is the fluid level now OK? | -- | Go to Step 3 | -- | ||||||||
3 |
While the TCC Duty Cycle is 0 percent, does Tech 2 display a TCC slip speed within the specified range? | -20 to +20 RPM | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections | ||||||||
4 |
Is voltage reading greater than the specified value? | 6.0 Volts | Go to Step 6 | Go to Step 5 | ||||||||
5 |
Does either check indicate an open circuit or short to ground in the wiring? | -- | Repair open or short to ground in relevant circuit. Go to Step 17 | Go to Step 11 | ||||||||
6 |
Is voltage reading less than the specified value? | 0.3 Volts | Go to Step 7 | Go to Step 8 | ||||||||
7 |
Is resistance reading greater than the specified value? | 500 kΩ | Go to Step 9 | Go to Step 12 | ||||||||
8 | Using a digital voltmeter, check the wiring for a short to voltage condition between transmission wiring harness TCM connector A112-T68, terminal X1-4 and connector X121-X1, terminal X1-20. Does the check indicate a short to voltage in the wiring? | -- | Repair short to voltage in relevant circuit. Go to Step 17 | -- | ||||||||
9 |
Is the resistance reading within the specified value? | 10.0-11.5 Ω @ 20°C 11.8-13.6 Ω @ 70°C | Go to Step 10 | If reading is more than specified, go to Step 13. If reading is less than specified, go to Step 14. | ||||||||
10 |
Does solenoid click as jumper wire is connected and disconnected? | -- | Go to Step 11 | Replace faulty TCC PWM solenoid. Refer to Torque Converter Clutch Solenoid Replacement | ||||||||
11 | Replace the TCM. Refer to Refer to Transmission Control Module Replacement for replacement procedures. Is the replacement complete? | -- | Go to Step 17 | -- | ||||||||
12 | Using a digital voltmeter, check wiring for a short to ground condition between transmission wiring harness TCM connector A112-T68, terminal X1-4 and transmission wiring harness connector X121-X1, terminal X1-20. Does the check indicate a short to ground in the wiring? | -- | Repair short to voltage in relevant circuit. Go to Step 17 | -- | ||||||||
13 | Using a digital voltmeter, check wiring for an open circuit condition between transmission wiring harness TCM connector A112-T68, terminal X1-4 and transmission wiring harness connector X121-X1, terminal X1-20. Does the check indicate an open circuit or high resistance in the wiring? | -- | Repair cause of open circuit or high resistance in relevant circuit. Go to Step 17 | Go to Step 15 | ||||||||
14 | Using a digital voltmeter, check wiring for an internal short circuit condition between transmission wiring harness TCM connector A112-T68 and transmission wiring harness connector X121-X1 connector, circuits 1525 and 418. Does the check indicate an internal short circuit condition in the wiring? | -- | Repair cause of internal short circuit condition in circuits 1525 and 418. Go to Step 17 | Go to Step 15 | ||||||||
15 |
Is the transmission internal wiring harness OK? | -- | Go to Step 16 | Replace the transmission internal wiring harness. Refer to Transmission Internal Electrical Harness Replacement. Go to Step 17 | ||||||||
16 | With the fluid pan removed, inspect the front control valve body. Inspect for the following conditions:
Did you find any of the above conditions? | -- | Repair or replace components as necessary. Go to Step 17 | Go to Step 17 | ||||||||
17 | Perform the following procedure to verify the repair:
Operate the vehicle under the following conditions:
Drive the vehicle as noted above to cycle the TCC a second time. Has the test run and passed? | -- | Go to Step 18 | Go to Step 2 | ||||||||
18 | On the Tech 2, observe the stored information, capture information and DTC information. Does the Tech 2 display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | ||||||||||||
