P0748

DTC P0748 (Gas)











Circuit Description
The pressure control (PC) solenoid valve is a powertrain 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 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 percent or less than 1.9 percent, then DTC P0748 sets. DTC P0748 is a type C DTC.

Conditions for Running the DTC:
- The system voltage is greater than 11 volts at -40*C (-40'F) transmission fluid temperature or 12 volts at 150°C (302°F) transmission fluid temperature.
- The engine must be running for at least 7 seconds.

Conditions for Setting the DTC
The PC duty cycle exceeds 95 percent or is less than 0.5 percent for 0.7 seconds.

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 records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records.
- 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 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
- DTC P0748 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.
- Inspect the PC solenoid wiring for after-market products designed to alter transmission line pressure.

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 AT wiring harness assembly for correct resistance.
5. This step tests the PC solenoid valve and the internal wiring harness for a short to ground.
7. When performing this step refer to Product Service Bulletin #9474L80E-07 for PC Solenoid Valve Application.
8. This step tests the entire PC solenoid valve circuit up to the PCM for continuity.
11. This step tests for a short to ground in the PC solenoid valve high control circuit (CKT 1228) and the PC solenoid valve low control circuit (CKT 1229), of the engine harness.