P0748
P0748-PRESSURE SOL CONTROL/TRANS RELAY CIRCUITS (DIESEL)
For the Transmission circuit diagram Refer to Transmission Control Systems/Diagrams
For a complete wiring diagram refer to diagrams.
Theory of Operation
The Governor Pressure Solenoid is used to control governor pressure. Governor pressure is used to shift between first, second, and third gear.
- When Monitored:
Continuously with the ignition on.
- Set Condition:
This DTC will set if the ECM monitored voltage detected on the Governor Pressure Solenoid Control circuit is different than the expected voltage. Note: To clear this DTC, it is necessary to drive the vehicle at a sustained speed which would allow the TCC and/or Overdrive Clutch to operate.
Possible Causes
- FUSED B+ CIRCUIT OPEN
- (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
- (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT SHORT TO GROUND
- (T118) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT OPEN
- (T118) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT SHORT TO GROUND
- (T118) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT SHORT TO VOLTAGE
- (T118) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT SHORT TO ANOTHER CIRCUIT
- TRANSMISSION CONTROL RELAY - POOR CONTACTS
- GOVERNOR PRESSURE SOLENOID
- ENGINE CONTROL MODULE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. CHECK IF THE DTC P0882 IS PRESENT
Ignition on, engine not running.
With the scan tool, read Engine DTCs.
Is the DTC P0882 present also?
Yes >>Refer to the Transmission category and perform the appropriate symptom.
No >>Go To 2
2. CHECK IF THE DTC IS CURRENT
With the scan tool, read Engine DTCs.
Record the Freeze Frame data for the reported DTC.
With the scan tool, erase DTCs.
Turn the ignition off to the lock position.
Using the Freeze Frame data recorded earlier, try to duplicate the conditions in which the DTC originally set.
NOTE: It may be necessary to road test the vehicle to duplicate the original set conditions. With the scan tool, read Engine DTCs.
Did the DTC reset?
Yes >>Go To 3
No >>Go To 12
3. CHECK THE (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT
Turn the ignition off to the lock position.
Disconnect the Transmission Solenoid Assembly harness connector.
NOTE: Check connectors - Clean/repair as necessary.
Ignition on, engine not running. With the scan tool, actuate the Transmission Control Relay.
Using a 12-volt test light connected to ground, check the (T16) Transmission Control Relay Output circuit in the Transmission Solenoid Assembly harness connector.
NOTE: The test light must illuminate brightly. Compare the brightness to that of a direct connection to the battery.
Does the test light cycle on and off and illuminate brightly?
Yes >>Go To 4
No >>Go To 9
4. CHECK THE ((T118)) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT FOR AN OPEN
Turn the ignition off to the lock position.
Disconnect the Transmission Solenoid Assembly harness connectors. Disconnect the ECM C2 harness connector.
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance of the ((T118)) Governor Pressure Solenoid Control circuit between the Transmission Solenoid Assembly harness connector and the ECM C2 harness connector.
Is the resistance below 5.0 ohms?
Yes >>Go To 5
No >>Repair the ((T118)) Governor Pressure Solenoid Control circuit for an open.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
5. CHECK THE ((T118)) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT FOR A SHORT TO GROUND
Measure the resistance between ground and the ((T118)) Governor Pressure Solenoid Control circuit.
Is the resistance below 5.0 ohms?
Yes >>Repair the ((T118)) Governor Pressure Solenoid Control circuit for a short to ground.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Go To 6
6. CHECK THE ((T118)) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT SHORT TO VOLTAGE
Ignition on, engine not running.
Measure the voltage of the ((T118)) Governor Pressure Solenoid Control circuit.
Is the voltage above 0.5 volt?
Yes >>Repair the ((T118)) Governor Pressure Solenoid Control circuit for a short to voltage.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Go To 7
7. CHECK THE ((T118)) GOVERNOR PRESSURE SOLENOID CONTROL CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT.
Turn the ignition off to the lock position.
Remove the Transmission Control Relay.
Measure the resistance between the ((T118)) Governor Pressure Solenoid Control circuit and all other circuits in the Transmission Solenoid Assembly harness connector.
Is the resistance below 5.0 ohms between the ((T118)) Governor Pressure Solenoid Control circuit and any other circuit in the Transmission Solenoid Assembly harness connector?
Yes >>Repair the ((T118)) Governor Pressure Solenoid Control circuit for a short to another circuit(s).
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Go To 8
8. CHECK THE GOVERNOR PRESSURE SOLENOID
Remove the Transmission Oil Pan per the Service Information.
Check all internal wiring pertaining to the Governor Pressure Solenoid for an open, short, and bent or broken terminals.
If no internal wiring problems are found, replace the Governor Pressure Solenoid per the Service Information.
Drive the vehicle performing multiple upshifts and downshifts.
With the scan tool, read Transmission DTCs.
Does the DTC reset?
Yes >>Using the schematics as a guide, check the Engine Control Module (ECM) 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 and program the ECM per the Service Information.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Test Complete.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
9. CHECK THE FUSED B(+) CIRCUIT
Turn the ignition off to the lock position. Remove the Transmission Control Relay. Ignition on, engine not running. Using a 12-volt test light connected to ground, check the Fused B(+) circuit in the Transmission Control Relay connector.
Does the test light illuminate brightly?
Yes >>Go To 10
No >>Repair the Fused B(+) circuit for an open. If the fuse is open, make sure to check for a short to ground.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
10. CHECK THE (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT FOR A SHORT TO GROUND
Turn the ignition off to the lock position.
Disconnect the Transmission Solenoid Assembly harness connector.
Measure the resistance between ground and the (T16) Transmission Control Relay Output circuit.
Is the resistance below 5.0 ohms?
Yes >>Repair the (T16) Transmission Control Relay Output circuit for a short to ground.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Go To 11
11. CHECK THE (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
Connect a jumper wire between Fused B(+) and the (T16) Transmission Control Relay Output circuit in the Transmission Control Relay connector.
Ignition on, engine not running.
Using a 12-volt test light connected to ground, check the (T16) Transmission Control Relay Output circuit in the Transmission Solenoid Assembly harness connector.
Does the test light illuminate brightly?
Yes >>Replace the Transmission Control Relay.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Replace the (T16) Transmission Control Relay Output circuit for an open.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL).
12. INTERMITTENT WIRING AND CONNECTORS
The conditions necessary to set this DTC are not present at this time.
Use the Freeze Frame Data to help duplicate the conditions in which the DTC originally set. Pay particular attention to the DTC set conditions, such as, VSS, MAP, ECT, and Load
Using the schematics as a guide, visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.
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 RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Test Complete.