P0778-SHIFT PRESSURE SOLENOID CIRCUIT

For a complete wiring diagram Refer to Section 8W

Theory of Operation

The Shift Pressure Solenoid is activated when the Transmission Control Module (TCM) determines that a transmission gear shift is required. The Shift Pressure Solenoid is pulse width modulated (PWM) controlled to allow the proper amount of hydraulic pressure to the shift elements. The Shift Pressure Solenoid is only activated during the shift of the transmission. When the Shift Pressure Solenoid is activated, hydraulic pressure is applied to the proper shift elements through one of the shift solenoids in the transmission to allow the desired shift. Once the shift is completed the solenoid is turned off.

• When Monitored:

  When the Shift Pressure Solenoid is: off, or active with 25-75% duty cycle, and the Solenoid Supply voltage is active.

• Set Condition:

  When Shift Pressure Solenoid is turned on and the TCM detects any of the following in the Shift Pressure Solenoid or circuit: open, short to ground, short to voltage, or the solenoid driver in the TCM.

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 the 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

• Go To 3

• Repair the (T77) Shift Pressure Solenoid Control circuit for an open.
• Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

• Repair the (T77) Shift 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 (T77) Shift Pressure Solenoid Control circuit for 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 Shift Pressure Solenoid 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.