P0748

Circuit Description
The pressure control solenoid valve (PC Solenoid Valve) regulates actuator feed fluid passing through the solenoid into torque signal pressure. The Powertrain Control Module (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 Solenoid Valve from 0.1-1.1 amp. An internal current monitor within the PCM proviies feedback in order to determine actual PC Solenoid 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 PC Solenoid Valve is enabled.
^ The system voltage is:
- Greater than 11 volts at a low temperature -40°C (-40°F).
- Greater than 13 volts at a high temperature 151°C (304°F).
^ The PCM commands the PC Solenoid Valve ON and the circuit voltage remains high (B+).
^ The PCM commands the PC Solenoid Valve OFF and the circuit voltage remains low (0 volts).

Action Taken When the DTC Sets
^ The PCM does not illuminate the Malfunction Indicator Lamp (MIL).
^ The PCM commands 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 the PCM history.
^ The PCM clears the DTC from the PCM history if the vehicle completes 40 consecutive warm-up cycles without an 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 20-way connector, the PC Solenoid Valve connector and all other circuit connecting points for the following conditions:
- A bent terminal.
- A backed out terminal.
- A damaged terminal.
- Poor 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.
^ 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 Solenoid Valve.
3. This step verifies that the automatic transmission wiring harness assembly (A/T Wiring Harness Assembly) and the PC Solenoid Valve have correct resistance.
7. This step tests for a short to ground inside the transmission.
8. This step tests circuits 1228 (PPL) and 1229 (LT BLU) of the A/T Wiring Harness Assembly for a short to ground.
10. This step tests circuit 1229 (LT BLU/WHT) from the engine 20-way connector to the PCM for an open.
15. This step tests circuit 1228 (RED/BLK) from the engine 20-way connector to the PCM for a short to ground.
17. This step tests circuit 1228 (RED/BLK) from the engine 20-way connector to the PCM for an open.