P0748

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Pressure Control Solenoid Valve (PC Sol. Valve) is an electronic device that regulates transmission line pressure based on the current flow through its coil winding. The magnetic field Produced by the coil moves the solenoid's internal valve which varies pressure to the pressure regulator valve. The Vehicle Control Module (VCM) controls the PC Sol. Valve by applying a varying amount of amperage to the solenoid. The applied amperage can vary from 0.1 to 1.1 amps. Low amperage (0.1 amp) indicates high line pressure. High amperage (1.1 amps) indicates low line pressure. The duty cycle of the PC Sol. Valve is expressed as a percentage of energized ON time. Zero percent indicates zero ON time (non-energized) or no current flow. Approximately 60% at idle indicates maximum ON time (energized) or high current flow. The VCM determines the appropriate line pressure for a given load by comparing the Throttle Position (TP) voltage, the engine speed and other inputs.

When the VCM detects a continuous open or short to ground in the PC Sol. Valve circuit or the PC Sol. Valve, then DTC P0748 sets. DTC P0748 is a type D DTC.

CONDITIONS FOR SETTING THE DTC

^ The system voltage is 10-16 volts.

^ The engine is running.

^ The PC Sol. duty cycle reaches its high limit (approximately 95%) or low limit (approximately 0%).

ACTION TAKEN WHEN THE DTC SETS

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

^ The VCM freezes shift adapts from being updated.

^ The PC Sol. Valve is OFF.

^ DTC P0748 stores in VCM history.

CONDITIONS FOR CLEARING THE DTC

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

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

DIAGNOSTIC AIDS

^ Inspect the wiring at the VCM, the transmission 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 condition, massage the wiring harness while watching the test equipment for a change.

^ DTC P0748 may set under low voltage conditions caused by high electrical system demands.

TEST DESCRIPTION

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

2. This step tests the ability of the VCM to command the PC Sol. Valve.

3. This step tests the PC Sol. Valve and Automatic Transmission Wiring Harness Assembly (A/T Wiring Harness Assembly) for incorrect resistance.