P0748

Circuit Description
The Pressure Control (PC) solenoid valve is a Vehicle Control Module (PCM) controlled device that regulates the transmission line pressure. The PCM compares Throttle Position (TP) sensor voltage, engine RPM, and other inputs in order to determine the appropriate line pressure for a given load. The PCM regulates the line pressure by applying a varying duty cycle to the PC solenoid valve based on the resistance of the solenoid, and the amperage needed to obtain optimum line pressure. The applied amperage varies from 0.1 amps for maximum line pressure to 1.1 amps for minimum line pressure.

If the PCM detects a PC duty cycle that exceeds 95% or is less than 1.9%, then DTC P0748 sets. DTC P0748 is a type D DTC.

1mConditions for Running the DTC
^ The system voltage is greater than 10 volts at -40°C TFT or 12.5 volts at 150°C TFT.
^ The engine must be running greater than 475 RPM for at least 7 seconds, and not in fuel cut-off..

Conditions for Setting the DTC
^ The PC duty cycle exceeds 95% or is less than 1.9%.
^ All conditions met for 200 milliseconds (0.2 second).

Action Taken When the DTC Sets
^ The PCM does not illuminate the Malfunction Indicator Lamp (MIL).
^ The PCM disables the PC solenoid valve, defaulting the transmission to maximum line pressure.
^ The PCM freezes shift adapts.
^ The PCM stores DTC P0748 in PCM history.

Conditions for Clearing the DTC
^ A scan tool clears the DTC from PCM history.
^ The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission-related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids
^ Inspect the wiring at the PCM, the transmission connector and all other circuit connecting points for the following conditions:
- A backed out terminal
- A damaged terminal
- Reduced terminal tension
- A chafed wire
- A broken wire inside the insulation
- Moisture intrusion
- Corrosion
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ Inspect for any transmission DTCs that may have reset.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests the ability of the PCM to command the PC solenoid valve.
3. This step tests the PC solenoid valve and the automatic transmission wiring harness assembly for incorrect resistance.
6. This step tests the PC solenoid valve and the internal wiring harness for a short to ground.
8. When performing this step refer to Product Service Bulletin #9474L80E-07 for PC solenoid valve application.
9. This step tests the entire PC solenoid valve circuit for proper resistance.
10. This step tests for a short to ground in circuits 1228 and 1229 of the engine harness.