For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0973 : 1-2 Shift Solenoid (SS) Control Circuit Low Voltage
DTC P0976: 2-3 Shift Solenoid (SS) Control Circuit Low Voltage
DTC P0979: 4-5 Shift (SS) Control Circuit Low Voltage
DTC P2764: Torque Converter Clutch (TCC) Pressure Control (PC) Solenoid Control Circuit Low Voltage

### Circuit/System Description

The 1-2 shift solenoid (SS) valve, 2-3 SS valve and the 4-5 SS valve control transmission fluid pressure acting on the shift valves to position the valves for the appropriate gear. The 1-2 SS, 2-3 SS and the 4-5 SS valves are located on the control valve body. The transmission control module (TCM) commands the solenoid ON or OFF by switching the ground path. The TCM provides voltage to the solenoid through high side driver 2 (HSD2). When the 1-2 SS valve, 2-3 SS or the 4-5 SS valve is commanded ON, the TCM senses low voltage. When the 1-2 SS valve, 2-3 SS or the 4-5 SS valve is commanded OFF, the TCM senses high voltage. The torque converter clutch pulse width modulated (TCC PWM) solenoid valve is a solenoid used to control the application and release of the converter clutch. The TCM provides voltage to the TCC PWM solenoid valve through HSD2. When the solenoid is commanded OFF, the TCM senses high voltage. When the solenoid is commanded ON, the TCM senses low voltage.

### Conditions for Running the DTC

• | The engine run time is greater than 5 seconds.

• | HSD2 is commanded ON.

### Conditions for Setting the DTC

#### P0973

The following conditions occur for 4.3 seconds:

• | The TCM detects an open in the 1-2 shift solenoid valve circuit when HSD2 is commanded ON.

• | The TCM detects a short to ground in the 1-2 shift solenoid valve circuit when HSD2 is commanded OFF.

#### P0976

The following conditions occur for 4.3 seconds:

• | The TCM detects an open in the 2-3 shift solenoid valve circuit when HSD2 is commanded ON.

• | The TCM detects a short to ground in the 2-3 shift solenoid valve circuit when HSD2 is commanded OFF.

#### P0979

The following conditions occur for 4.3 seconds:

• | The TCM detects an open in the 4-5 shift solenoid valve circuit when HSD2 is commanded ON.

• | The TCM detects a short to ground in the 4-5 shift solenoid valve circuit when HSD2 is commanded OFF.

#### P2764

The following conditions occur for 4.3 seconds:

• | The TCM detects an open in the TCC PWM solenoid valve circuit when the PWM duty cycle is at least 20 percent.

• | The TCM detects a short to ground in the TCC PWM solenoid valve circuit when the PWM duty cycle is 20-50 percent.

### Action Taken When the DTC Sets

#### P0973

• | DTC P0973 is a Type B DTC.

• | Powertrain braking is disabled at the time that the TCM first detects the failure, before the DTC sets.

• | The TCM turns off power to all solenoids.

• | The transmission will operate in fifth gear if the vehicle has successfully completed a 1-2 upshift in the current ignition cycle. If the vehicle has not completed a 1-2 upshift in the current ignition cycle, the transmission will operate in fourth gear.

• | The TCM commands maximum line pressure.

• | The TCM freezes transmission adaptive functions.

• | The TCM inhibits TAP shift.

#### P0976

• | DTC P0976 is a Type B DTC.

• | Powertrain braking is disabled at the time that the TCM first detects the failure, before the DTC sets.

• | The TCM turns off power to all solenoids.

• | The transmission will operate in fifth gear if the vehicle has successfully completed a 1-2 upshift in the current ignition cycle. If the vehicle has not completed a 1-2 upshift in the current ignition cycle, the transmission will operate in fourth gear.

• | The TCM commands maximum line pressure.

• | The TCM freezes transmission adaptive functions.

• | The TCM inhibits TAP shift.

#### P0979

• | DTC P0979 is a Type B DTC.

• | Powertrain braking is disabled at the time that the TCM first detects the failure, before the DTC sets.

• | The TCM turns off power to all solenoids.

• | The transmission will operate in fifth gear if the vehicle has successfully completed a 1-2 upshift in the current ignition cycle. If the vehicle has not completed a 1-2 upshift in the current ignition cycle, the transmission will operate in fourth gear.

• | The TCM commands maximum line pressure.

• | The TCM freezes transmission adaptive functions.

• | The TCM inhibits TAP shift.

#### P2764

• | DTC P2764 is a Type B DTC.

• | The TCM turns off power to all solenoids.

• | The transmission will operate in fifth gear if the vehicle has successfully completed a 1-2 upshift in the current ignition cycle. If the vehicle has not completed a 1-2 upshift in the current ignition cycle, the transmission will operate in fourth gear.

• | The TCM commands maximum line pressure.

• | The TCM freezes transmission adaptive functions.

### Conditions for Clearing the DTC

DTC P0973, P0976, P0979 and P2764 are Type B DTCs.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Transmission General Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Transmission Control Module Scan Tool Information

#### Special Tools

• | J 35616 GM-Approved Terminal Test Kit

• | J 44152 Jumper Harness (20 Pins)

• | J 45681 Jumper Harness

### Circuit/System Verification

Start and idle the engine. Using the scan tool output controls command the 1-2 SS ON and OFF. Observing the 1-2 Sol. CKT Status parameter on the scan tool, ensure that the parameter shows OK.

### Circuit/System Testing

1. Inspect the TRANS fuse for an open.

⇒ | If the fuse is open, test the ignition 1 voltage circuit and the affected control circuit for a short to ground between the Fuse Block-Underhood and the AT inline 20-way connector.

2. Disconnect the AT inline 20-way connector. Connect the J 45681 jumper harness, to the engine side of the connector. Using the J 35616 GM-approved terminal test kit, connect a test lamp between the ignition 1 voltage circuit and the affected control circuit. Turn ON the ignition with the engine OFF. Using the scan tool output controls command the affected solenoid ON and OFF. The test lamp should blink ON and OFF as commanded.

⇒ | If the test lamp is always OFF, test the circuits for an open.

3. Connect the J 45681 to the transmission side of the connector. Using the J 35616 , measure the resistance between the ignition 1 voltage circuit and the affected control circuit. Resistance should be between 15-20.3 ohms for the 1-2 SS, 2-3 SS and the 4-5 SS. Resistance should be between 10-13.6 ohms for the TCC PWM solenoid valve.

⇒ | If resistance is greater than the specified range, test the circuits for an open. If the resistance is less than the specified range, test for a faulty solenoid or a shorted together condition.

4. Measure the resistance between the ignition 1 voltage circuit and the transmission case. The resistance should be greater than 50K ohms.

⇒ | If the resistance is less than 50K ohms, test the ignition 1 voltage circuit for a short to ground.

5. Measure the resistance between the affected control circuit and ground. The resistance should be greater than 50K ohms.

⇒ | If the resistance is greater than 50K ohms, test the affected control circuit for a short to ground.

### Component Testing

1. Using the J 44152 jumper harness (20 Pins), and the J 35616 , measure the resistance between the ignition 1 voltage circuit and the affected control circuit. The resistance should be between 19-31 ohms for the 1-2 SS and the 2-3 SS. The resistance should be between 10-15 ohms for the TCC PWM solenoid.

⇒ | If the resistance is not within the specified range, remove the oil pan.

2. Disconnect the wiring harness connector from the affected solenoid. Measure the resistance of the affected control circuit. The resistance should be between 19-31 ohms for the 1-2 SS and the 2-3 SS. The resistance should be between 10-15 ohms for the TCC PWM solenoid.

⇒ | If the resistance is not within the specified range, replace the affected solenoid.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• | 1-2 Shift Solenoid Valve Replacement

• | 2-3 Shift Solenoid Valve Replacement

• | 4-5 Shift Solenoid Valve Replacement

• | Torque Converter Clutch Solenoid Replacement

• | Transmission Internal Electrical Harness Replacement

• | Control Module References for TCM replacement, setup and reprogramming.