P0748

DTC P0748 Pressure Control Solenoid Circuit Electrical






Circuit Description

The Powertrain Control Module (PCM) uses the Pressure Control Solenoid Valve (PC Sol. Valve) in order to regulate the transmission line pressure. The PC Sol. Valve consists of an electrical connector, a coil, an armature, a regulating spring, and a poppet valve. The PC Sol. Valve is attached to the upper control body. The PCM compares TP voltage, fluid temperature, gear states, and other inputs in order to determine the line pressure appropriate for a given load. The PCM regulates the pressure by applying a varying amperage to the PC Sol. Valve. The applied amperage varies from 0.1 amps for maximum lime pressure to 1.1 amps for minimum line pressure. The PCM then monitors the amperage at the return line.

When the PCM 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 9-16 volts.
- The PC Sol. Valve duty cycle is 0% or greater than 95%.

Action Taken When the DTC Sets

- The PCM does not illuminate the Malfunction Indicator Lamp (MIL).
- The PCM commands maximum line pressure (0 amps).
- The PCM freezes shift adapts from being updated.
- DTC P0748 is stored in the PCM history.

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 2-way connector. Look 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.
- Extended engine cranking with a weak 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 1228 from the engine 20-way connector to the PC Sol. Valve 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 1229 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 a short to ground.
20. When DTC P0748 sets, the PCM commands maximum line pressure and does not inhibit TCC engagement. This can lead to excessive heat build-up, causing the Torque Converter to "balloon." You must replace the Torque Converter.