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 (5L40-E) (Transmission Control Module Scan Tool Information (5L40-E))Transmission Control Module Scan Tool Information (6L50/6L80/6L90) (Transmission Control Module Scan Tool Information (6L50/6L80/6L90))
Special Tools
* J 35616 GM-Approved Terminal Test Kit
* J 45681 Jumper Harness
Circuit/System Testing
1. Using the scan tool, increase and decrease the PC solenoid amperage. Observe the scan tool display.
• If the PC Sol. Actual Current varies from the PC Sol. Ref. Current by more than 0.05 amps, turn OFF the ignition.
2. Disconnect the AT 20-way inline connector. Using the J 45681 jumper harness, and the J 35616 GM-approved terminal test kit, measure the resistance between the PC Solenoid valve high control circuit and the PC Solenoid valve 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.
3. Test the high and low control circuit of the PC Solenoid for a short together.
• If the voltage is not near the specified value, repair the open or high resistance in the TFT sensor signal circuit.
4. Measure the voltage between the TFT sensor signal circuit and the low reference circuit at the AT 20-way inline connector. The voltage should be near 5 volts.
• If the voltage is not near the specified value, repair the open or high resistance in the low reference circuit.
5. Using the J 45681 , measure the resistance between the TFT sensor signal circuit and the low reference circuit at the transmission side of the AT 20-way inline connector. Refer to Temperature Versus Resistance. The resistance should be between the specified range for the given temperature.
• If the resistance is not within the specified range for the given temperature, replace the TFT sensor.
Component Testing
1. Disconnect the AT 20-way inline connector and measure the resistance between the TFT sensor signal circuit and the low reference circuit. Refer to Temperature Versus Resistance for resistance values.
• If the resistance is not within the specified range for the given temperature, replace the TFT sensor.
2. Test the TCM for supplying the 5-volt reference circuit to the TFT sensor.
• If the TCM is not supplying a 5-volt reference to the TFT sensor, replace the TCM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Manual Shift Shaft Position Switch Replacement (5L40-E/5L50-E - Automatic Transmission)
* Refer to Control Module References (Programming and Relearning) for TCM replacement, setup, and programming.
* Transmission Internal Electrical Harness Replacement (Service and Repair)