P0748-MODULATOR PRESSURE SOLENOID CIRCUIT

For a complete wiring diagram Refer to Section 8W

Theory of Operation

The Modulating Pressure Control Solenoid Valve's purpose is to control the modulating pressure depending on the continuously changing operating conditions, such as load and gear change.

The Modulating Pressure Control Solenoid Valve is always active. The solenoid uses pulse width modulation (PWM) to control the transmissions hydraulic fluid pressure that is determined by the Transmission Control Module (TCM).

• When Monitored:

  Continuously with the ignition on, engine running, the Modulating Pressure Control Solenoid Valve is either off, or active with 25-75% duty cycle, with no Solenoid Supply Voltage DTCs present.

• Set Condition:

  When the Modulating Pressure Control Solenoid Valve is turned on and the Solenoid driver detects an error (the measured current is too different then the target current) or when the solenoid is off and a short to ground is detected.

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

Diagnostic Test

NOTE: When the Transmission Control Module (TCM) detects and stores a DTC, the TCM also stores the vehicles operating conditions under which the DTC originally set. This information is located in scan tool under Environmental Data. Before erasing any stored DTCs, record any available data to assist in duplicating the conditions in which the DTC originally set.

• Go To 2

• Go To 6

• Repair the (T76) Modulation Pressure Solenoid Control circuit for an open.
• Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

• Go To 3

• Repair the (T76) Modulation Pressure Solenoid Control circuit for a short to ground.
• Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

• Go To 4

• Repair the (T76) Modulation Pressure Solenoid Control circuit for a short to another circuit.
• Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

• Go To 5

• Using the schematics as a guide, check the Transmission Control Module (TCM) pins, terminals, and connectors for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the TCM per the Service Information. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/TRANSMISSION CONTROL MODULE - REMOVAL)
• Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

• Replace the Modulating Pressure Control Solenoid Valve per the Service Information.
• Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

• Repair as necessary.
• Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

• Test Complete.