P0748

Circuit Description

The Pressure Control Solenoid Valve (PC Sol. Valve) regulates actuator feed fluid passing through the solenoid into torque signal pressure. The PCM uses a pulse width modulated signal in order to control the torque signal pressure. The PCM compares various inputs in order to determine the appropriate pressure for a given load. The PCM varies the current to the PC Sol. Valve from 0.1-1.1 amp. An internal current monitor within the PCM provides feedback in order to determine actual PC Sol. Valve current draw.

If the PCM detects a commanded current draw that differs from the actual current draw by more than a calibrated value, then DTC P0748 sets. DTC P0748 is a Type D DTC.


Conditions for Setting the DTC

^ The Pressure Control Solenoid (PC Sol.) Valve is enabled.

^ The system voltage is:

- Greater than 9.0 volts (or 9.5 volts, depending upon the temperature).

- Greater than 10.0 volts (or 10.5 volts, depending upon the temperature) after dropping below 9.0 volts (or 9.5 volts, depending upon the temperature).

^ The PCM commands the PC Sol. valve ON and the circuit voltage remains high (B+).

^ The PCM commands the PC Sol. valve OFF and the circuit voltage remains low (0 volts).


Action Taken When the DTC Sets

^ The PCM commands maximum line pressure.

^ The PCM disables shift adapts.

^ The PCM does not illuminate the Malfunction Indicator Lamp (MIL).


Conditions for Clearing the DTC

^ A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

Diagnostic Aids

^ Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the transmission 20-way connector. Inspect the wiring for poor electrical connections at the PC Sol. Valve connector. Look for the following problems:

- A bent terminal

- A backed out terminal

- A damaged terminal

- Poor terminal tension

- A chafed wire

- A broken wire inside the insulation

^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

^ Extended cranking with a low battery could set DTC P0748.

Test Description

The numbers below refer to the Step numbers on the diagnostic table.

2. This step verifies the ability of the PCM to command the PC Sol. Valve.

3. This step verifies that the Automatic Transmission Wiring Harness Assembly and the PC Sol. Valve have correct resistance.

7. This step tests circuit 1229 of the A/T Wiring Harness Assy. for a short to ground.

8. This step tests circuit 1229 from the engine 20-way connector to the PCM for a short to ground.

10. This step tests circuit 1229 from the engine 20-way connector to the PCM for an open.

11. This step tests circuit 1228 from the engine 20-way connector to the PCM for a short to ground.

15. This step tests circuit 1228 from the engine 20-way connector to the PCM for an open.