P0748

DTC P0748

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

DTC Descriptor
DTC P0748
- Pressure Control (PC) Solenoid Control Circuit

Circuit/System Description

The pressure control (PC) solenoid valve regulates actuator feed fluid passing through the solenoid into torque signal pressure. The transmission control module (TCM) uses a pulse width modulated signal in order to control the torque signal pressure. The TCM compares various inputs in order to determine the appropriate pressure for a given load. The TCM varies the current to the PC solenoid from 0.1 amps, for maximum line pressure to 1.1 amps, for minimum line pressure. An internal current monitor within the TCM provides feedback in order to determine actual PC solenoid valve current draw.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The PC solenoid valve feedback circuit indicates a continuous open or short to ground for 1.2 seconds or greater.

Action Taken When the DTC Sets

* DTC P0748 is a Type C DTC.
* The TCM commands maximum line pressure.
* The TCM freezes transmission adaptive functions.

Conditions for Clearing the DTC

DTC P0748 is a Type C DTC.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Transmission General Description (Transmission General Description)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Transmission Control Module Scan Tool Information (Transmission Control Module Scan Tool Information)
Special Tools

* J 35616 GM-Approved Terminal Test Kit
* J 45681 Jumper Harness

Circuit/System Verification

Using the scan tool, command several values of solenoid reference current from 0.1-1.1 amps and observe the PC Sol. Actual Current and the PC Sol. Ref. Current. The PC Sol. Actual Current should not vary from the PC Sol. Ref. Current by greater than 0.16 amp.

Circuit/System Testing

1. Disconnect the automatic transmission inline 20-way connector. Install the J 45681 jumper harness, on the transmission side on the connector. Using the J 35616 GM-approved terminal test kit, measure the resistance between the PC Solenoid high control circuit and the PC Solenoid low control circuit.

• If the resistance is within 3.5-5.5 ohms, measure the resistance from the PC Sol. Valve high control circuit to ground.

• If the resistance is greater than 5.5 ohms, test the high and low control circuit of the PC Solenoid for an open.

2. Measure the resistance between the PC solenoid high control circuit and the transmission case. Measure the resistance between the PC solenoid low control circuit and the transmission case. The resistance should be greater than 50K ohms.

• If the resistance is less than 50K ohms, replace the automatic transmission wiring harness assembly.

3. Measure the resistance between the PC solenoid high control circuit and all other circuits of the J 45681 , except the PC solenoid low control circuit. Measure the resistance between the PC solenoid low control circuit and all other circuits of the J 45681 , except the PC solenoid high control circuit. The resistance should be greater than 10 ohms.

• If the resistance is less than 10 ohms, replace the automatic transmission wiring harness assembly.

4. Remove the J 45681 from the transmission side and install the J 45681 on the engine side of the harness. Disconnect the TCM connector. Using the J 35616 , measure the resistance of the PC solenoid high control circuit between the TCM connector and the automatic transmission inline 20-way connector. Measure the resistance of the PC solenoid low control circuit between the TCM connector and the automatic transmission inline 20-way connector. The resistance should be less than 10 ohms for each circuit.

• If the value is greater than 10 ohms repair the open in the affected circuit.

5. Measure the resistance between the PC solenoid high control circuit and ground. Measure the resistance between the PC solenoid low control circuit and ground. The resistance for each circuit should be greater than 10 ohms.

• If the value is less than 10 ohms repair the short to ground in the affected circuit.

6. Connect the TCM connector. Turn ON the ignition, with the engine OFF. Test the PC solenoid high control circuit and the PC solenoid low control circuit for a short to voltage.

• If a short to voltage condition is found, repair as necessary.

7. If all circuits/connections test normal, test or replace the PC solenoid valve.

Component Testing

Verify the PC solenoid valve resistance is between 3.5-5.5 ohms.

If the resistance is not within the specified range, replace the PC solenoid valve.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Pressure Control Solenoid Valve Replacement (Service and Repair)
* Transmission Internal Electrical Harness Replacement (Service and Repair)
* Refer to Control Module References (Programming and Relearning) for TCM replacement, setup, and programming