P0778
P0778-SHIFT PRESSURE SOLENOID CIRCUIT
For a complete wiring diagram Refer to Diagrams/Electrical Electrical Diagrams
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 2-3 Solenoid Control circuit: open, short to ground, short to voltage, or a faulty Shift Pressure Solenoid Control driver in the TCM.
Always perform the NAG1 Pre-Diagnostic Troubleshooting procedure before proceeding. NAG1 - Pre-Diagnostic Troubleshooting Procedure
Diagnostic Test
1. CHECK IF THE DTC IS CURRENT
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.
Turn the ignition off to the lock position.
With the scan tool, erase Transmission DTC's.
Using the Environmental Data recorded earlier, try to duplicate the conditions in which the DTC originally set. It may be necessary to test drive the vehicle.
With the scan tool, read Transmission DTC's.
Did the DTC P0778 reset?
Yes
- Go To 2
No
- Go To 6
2. CHECK THE (T77) SHIFT PRESSURE SOLENOID CONTROL CIRCUIT FOR AN OPEN
Turn the ignition off to the lock position.
Disconnect the TCM C2 harness connector.
Disconnect the Transmission Electrohydraulic Control Unit Assembly harness connector.
Measure the resistance of the (T77) Shift Pressure Solenoid Control circuit between the TCM C2 harness connector and the Transmission Electrohydraulic Control Unit Assembly harness connector.
Is the resistance below 5.0 ohms?
Yes
- Go To 3
No
- Repair the (T77) Shift Pressure Solenoid Control circuit for an open.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test
3. CHECK THE (T77) SHIFT PRESSURE SOLENOID CONTROL CIRCUIT FOR A SHORT TO GROUND
Measure the resistance between ground and the (T77) Shift Pressure Solenoid Control circuit.
Is the resistance below 5.0 ohms?
Yes
- Repair the (T77) Shift Pressure Solenoid Control circuit for a short to ground.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test
No
- Go To 4
4. CHECK THE (T77) SHIFT PRESSURE SOLENOID CONTROL CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT
Measure the resistance between the (T77) Shift Pressure Solenoid Control circuit and every other circuit in the Transmission Electrohydraulic Control Unit Assembly harness connector.
Is the resistance below 5.0 ohms between the (T77) Shift Pressure Solenoid Control circuit and any other circuit(s) in the Transmission Electrohydraulic Control Unit Assembly harness connector?
Yes
- Repair the (T77) Shift Pressure Solenoid Control circuit for a short to another circuit(s).
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test
No
- Go To 5
5. CHECK THE SHIFT PRESSURE SOLENOID
Reconnect the Transmission Electrohydraulic Control Unit Assembly harness connector.
Measure the resistance of the Shift Pressure Solenoid between the (T77) Shift Pressure Solenoid Control circuit and the (T78) Solenoid Voltage Supply circuit in the TCM C2 harness connector.
Is the resistance between 2.5 and 6.5 ohms?
Yes
- Using the schematics as a guide, check the Transmission Control Module (TCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the TCM.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test
No
- Replace the Shift Pressure Solenoid.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test
6. INTERMITTENT WIRING AND CONNECTORS
The conditions necessary to set this DTC are not present at this time.
Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
Wiggle the wiring and connectors while checking for any possible open or shorted circuits.
Check for any Service Information Tune-ups or Technical Service Bulletins that may apply.
Were there any problems found?
Yes
- Repair as necessary.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test
No
- Test Complete.