P0748
P0748-MODULATOR PRESSURE SOLENOID CIRCUIT
For a complete wiring diagram, refer to the Wiring Information.
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 NAG1 Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.
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 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.
1. Turn the ignition off to the lock position.
2. With the scan tool, erase Transmission DTCs.
3. 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.
4. With the scan tool, read Transmission DTCs.
Did the DTC P0748 reset?
Yes
- Go To 2
No
- Go To 6
2. CHECK THE (T76) MODULATION PRESSURE SOLENOID CONTROL CIRCUIT FOR AN OPEN
1. Turn the ignition off to the lock position.
2. Disconnect the TCM C2 harness connector.
3. Disconnect the Transmission Electrohydraulic Control Unit Assembly harness connector.
NOTE: Check connectors - Clean/repair as necessary.
4. Measure the resistance of the (T76) Modulation Pressure Solenoid Control circuit between the TCM C2 harness connector and the Transmission Electrohydraulic Control Unit Assembly harness connector.
Is the resistance above 5.0 Ohms?
Yes
- Repair the (T76) Modulation Pressure Solenoid Control circuit for an open.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.
No
- Go To 3
3. CHECK THE (T76) MODULATION PRESSURE SOLENOID CONTROL CIRCUIT FOR A SHORT TO GROUND
1. Measure the resistance between ground and the (T76) Modulation Pressure Solenoid Control circuit.
Is the resistance below 5.0 Ohms?
Yes
- Repair the (T76) Modulation 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 (T76) MODULATION PRESSURE SOLENOID CONTROL CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT
1. Measure the resistance between the (T76) Modulation Pressure Solenoid Control circuit and every other circuit in the Transmission Electrohydraulic Control Unit Assembly harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Repair the (T76) Modulation Pressure Solenoid Control circuit for a short to another circuit.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.
No
- Go To 5
5. CHECK THE MODULATING PRESSURE CONTROL SOLENOID VALVE
1. Reconnect the Transmission Electrohydraulic Control Unit Assembly harness connector.
2. Measure the resistance between the (T76) Modulation Pressure Solenoid Control circuit and the (T78) Solenoid Supply Voltage 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) connectors and terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the TCM.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.
No
- Replace the Modulating Pressure Control Solenoid Valve.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.
6. INTERMITTENT WIRING AND CONNECTORS
1. The conditions necessary to set this DTC are not present at this time.
2. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
3. Wiggle the wiring and connectors while checking for any possible open or shorted circuits.
4. 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.