For 1990-2009 cars

### DTC P0748 - Transaxle Line Pressure High

### Circuit Description

The pressure control (PC) solenoid is used to control main line pressure to the transaxle hydraulic system. The powertrain control module (PCM) pulse width modulates (PWM) the PC solenoid whenever the engine is running. The PCM controls the PC solenoid by pulse width modulating an internal driver that pulls the solenoid circuit to ground. When the PC solenoid is commanded Off, main line pressure is highest. During normal shift operation, the PCM will turn ON or OFF the 2, 3 or 4 shift solenoids and PWM the PC solenoid to prevent clutch slip and harsh shifts. The PC solenoid circuit is monitored for low and high voltage faults. The PCM also monitors main line pressure for high pressure. The PCM calculates main line pressure based on shift time and clutch slip. DTC P0748 sets when the PCM has commanded low main line pressure, but shift times for all gears are still too short indicating high main line pressure.

### DTC Parameters

DTC P0748 will set if the PCM has detected high main line pressure for 5 shifts when:

• | The upshift pressure error has reached the lower limit of less than -288 kPa.

• | The low engine load, low commanded main line pressure.

• | The TFT is greater than 40°C (104°F).

DTC P0748 diagnostic runs continuously when the above conditions have been met.

DTC P0748 is a type D DTC.

### Diagnostic Aids

Important: If DTC P0702, P0746 or P0747 is set, diagnose that DTC first. A diagnosed PC solenoid circuit DTC may have caused DTC P0748 to set.

Refer to Part Description and Pressure Port Air-Check for component location/description and main line pressure specifications and test procedures.

Upshift pressure error that is negative means the PCM is removing main line pressure, similar to fuel trim. Nominal value = 0 kPa.

Make sure the PC solenoid is not intermittently sticking. Audible sound should be similar for all solenoids. A muffled tone indicates the need for replacement.

An intermittent open anywhere or short to voltage on circuit 1530 will cause high main line pressure. Use scan tool to command PC SOLENOID ON (PWM) by performing SOLENOID AUDIBLE CHECK. Wiggling wires while performing test may locate a problem.

PC solenoid resistance: 3.8-7.2 ohms

Nominal value: 4.5 ohms at 68°F