P0748

Circuit Description
The PCM uses the pressure control (PC) solenoid valve in order to regulate the transmission line pressure. The PC solenoid valve consists of an electrical connector, a coil, an armature, a regulating spring, and a poppet valve. The PC solenoid 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 solenoid valve. The applied amperage varies from 0.1 amps for maximum line 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 solenoid valve circuit, or the PC solenoid valve, then DTC P0748 sets. DTC P0748 is a type D DTC.

Conditions for Running the DTC
The system voltage is 8-18 volts.

Conditions for Setting the DTC
The PC solenoid 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.
^ 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 consecutive 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
Inspect the wiring at the PCM, the transmission 20-way connector and the PC solenoid valve 2-way connector for the following conditions:
- A backed out terminal.
- A damaged terminal.
- Reduced 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 solenoid valve.
3. This step verifies that the automatic transmission wiring harness and the PC solenoid valve have correct resistance.