4T65-E Automatic Transaxle

DTC P0748















Circuit Description with 4T65-E Automatic Transaxle
The pressure control (PC) solenoid valve is located in the valve body. The PC solenoid valve controls transmission line pressure based on current flow through its windings. The PCM determines desired line pressure based on throttle position and other inputs. The PCM then varies the duty cycle on the high side of the PC solenoid valve to control current flow to the solenoid. Current is controlled from about 0.02 amps for maximum line pressure to 1.1 amps for minimum line pressure. The PCM monitors the actual current to the solenoid.
If the PCM detects a commanded current draw that differs from the actual current draw by more than a calibrated value, then DTC P0748 sets. DTC P0748 is a type C DTC.

Conditions for Running the DTC
^ The PC solenoid valve is enabled.
^ The system voltage is:
- Greater than 11 volts at a low temperature of -40°C (-40°F).
- Greater than 13 volts at a high temperature of 151°C (304°F).

Conditions for Setting the DTC
DTC P0748 sets when the duty cycle is outside the range of 0.5 - 95% for 0.2 seconds.

Action Taken When the DTC Sets
^ The PCM does not illuminate the malfunction indicator lamp (MIL).
^ The PCM enters PC solenoid valve diagnostic retest mode. The retest mode conducts the following diagnostic routine:
1. The PCM de-energizes the PC solenoid valve, resulting in maximum line pressure.
2. After being de-energized for 2 seconds, the PCM commands the PC solenoid valve ON at 0.1 amp for the retest period of 5 seconds.
^ If no circuit faults are detected during the 5 second retest period, then the PC solenoid valve is returned to normal operation and DTC P0748 diagnostic is passed.
If a circuit fault is detected 3 times during normal operation in the same ignition cycle, then the PCM de-energizes the PC solenoid valve for the remainder of that ignition cycle.
^ If a circuit fault is detected during the 5 second retest period, then the PCM de-energizes the PC solenoid valve for 2 seconds before reentering the retest mode.
If a circuit fault is detected 5 times without returning to normal operation, then the PC solenoid valve is de-energized for the remainder of that ignition cycle.
^ The PCM freezes shift adapts.
^ The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records.
^ The PCM stores DTC P0748 in PCM history.

Conditions for Clearing the DTC
^ A scan tool can clear the DTC.
^ The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies that the fault is present.
3. This step tests the transmission wiring harness and the PC solenoid valve for correct resistance.
9. This step begins diagnosis of the engine side of the circuit.