P0748

Diagnostic Chart:

Wiring Diagram:

During normal driving modes the PCM/TC adapts line pressure to prevent clutch slip and harsh shifts. This is accomplished by modulating the transmission fluid pressure (TFP) actuator ground (1530) to raise or lower pressure. Open circuit = high pressure, grounded circuit = low pressure. If the time required to make all shifts is too short and line pressure has been commanded low, it is determined that the actual line pressure is too high.

DTC PARAMETERS

DTC P0748 is set when the PCM has detected the following conditions for more than five shifts:

- Upshift pressure adaptive error is less than 112 which indicates over pressure. This condition must still exist after the up shift pressure adaptives have reached the lower limit (Low Limit = -288 kPa).

- Low load, low commanded pressure.

- Transaxle fluid temperature above 40°C (104°F).

TEST DESCRIPTION

Numbered steps below refer to numbered steps on chart.

1. Check for DTCs P0746, P0747, P0749, or P0702. They must be eliminated first as a possible cause of a DTC P0748.

2. Check actuator operation. Use actuator quick check. The actuator quick test will PWM the actuators at a set rate. Listen and compare noise of the TFP actuator to that of other actuators. The noise of all should be similar.

NOTE: To check actuator operation, command actuator quick test using the Scan tool.

3. Check pressure regulator valve operation. Make sure pressure increases in correct increments during pressure test. If pressure changes erratically or moves in large increments, the pressure regulator valve is probably sticking. Actuator Quick Chart

4. If little or no pressure change, the regulator valve is stuck. To verify, test for minimum and maximum oil pressure.

REPAIR VERIFICATION

Monitor DTC menu "Code Status" for "Pass Since Code Clear" and "Pass This Ignition Cycle." When both have passed, repair is verified.

Criteria for pass:

- Engine running.

- Power present at actuators and no active faults exist for this actuator.

DIAGNOSTIC AIDS

- When the PCM detects a fault in the circuit (open, ground, short) the PCM will open the circuit internally to protect the circuit.

- Could be a hot or cold only condition. If condition is intermittent, try to reproduce DTC by checking malfunction (MALF) history table with Scan tool to see at what temperature the DTC will set and reproduce conditions.

- This DTC may set or intermittent harsh upshifts may be caused by a poor electrical connection at either the PCM, actuator connector plate, or Under Hood Junction Block (UHJB) terminals. Wiggling connectors while performing an actuator quick test may isolate the problem area.