4L60-E / 4L65-E Automatic Transmission

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The Pressure Control (PC) solenoid valve is an electronic device that regulates transmission line pressure based on the current flow through its coil winding. The magnetic field produced by the coil moves the solenoid's internal valve which varies pressure to the pressure regulator valve. The Vehicle Control Module (VCM) controls the PC solenoid valve by applying a varying amount of amperage to the solenoid. The applied amperage can vary from 0.1 to 1.1 amps. Low amperage (0.1 amp) indicates high line pressure. High amperage (1.1 amps) indicates low line pressure. The duty cycle of the PC solenoid valve is expressed as a percentage of energized ON time. Zero percent indicates zero ON time (non-energized) or no current flow. Approximately 60% at idle indicates maximum ON time (energized) or high current flow. The VCM determines the appropriate line pressure for a given load by comparing the Throttle Position (TP) voltage, the engine speed and other inputs.

When the VCM detects a continuous open or short in the PC solenoid valve circuit, then DTC P0748 sets. DTC P0748 is a type C DTC.

CONDITIONS FOR RUNNING THE DTC
^ The system voltage is 10-19 volts.
^ The engine is running.

CONDITIONS FOR SETTING THE DTC
The PC solenoid valve duty cycle reaches its high limit (approximately 95%) or low limit (approximately 0%).

ACTION TAKEN WHEN THE DTC SETS
^ The VCM does not illuminate the Malfunction Indicator Lamp (MIL).
^ The PC solenoid valve is OFF.
^ The VCM freezes shift adapts from being updated
^ The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Failure Records.
^ The VCM stores DTC P0748 in VCM history.

CONDITIONS FOR CLEARING THE DTC
^ A scan tool can clear the DTC.
^ The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.
^ The VCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the VCM.

DIAGNOSTIC AIDS
^ Inspect the connectors at the VCM, the PC solenoid and all other circuit connecting points for an intermittent condition. Refer to Testing for intermittent and Poor Connections in Diagrams.
^ Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Diagrams.
^ DTC P0748 may set under low voltage conditions caused by high electrical system demands.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests the ability of the VCM to command the PC solenoid valve.
3. This step tests the PC solenoid valve and Automatic Transmission (AT) wiring harness assembly for incorrect resistance.