P1756
P1756-GOV PRESS NOT EQUAL TO TARGET @ 35 - 40 PSI (DIESEL)
For the Transmission circuit diagram Refer to Transmission Control Systems/Diagram.
For a complete wiring diagram refer to diagrams.
Theory of Operation
The Governor Pressure Control System is used to regulate the governor pressure which controls the shifts for first, second, and third gear. The Governor Pressure Control System test verifies that the requested pressure and the actual pressure are within a predetermined tolerance.
- When Monitored:
While driving and the commanded governor pressure is equal to the pressure required for third gear.
- Set Condition:
If the governor pressure sensor output is less than 407 kPa (60 psi) or greater than 621 kPa (80 psi) when the requested pressure is 407 - 621 kPa (60 - 80 psi) for 2.2 seconds. This DTC will set if there are two trips of five consecutive bad 2.2 second tests with the transmission oil temperature between 23.5 - 88°C (74 - 190°F).
Possible Causes
- OTHER TRANSMISSION DTCS PRESENT
- 5-VOLT SUPPLY CIRCUIT OPEN - EXTERNAL
- 5-VOLT SUPPLY CIRCUIT OPEN - INTERNAL
- - GOVERNOR PRESSURE SENSOR
- VALVE BODY
- INTERNAL TRANSMISSION
- ENGINE CONTROL MODULE
- TRANSMISSION - INTERNAL DAMAGE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. CHECK IF OTHER TRANSMISSION DTCS ARE PRESENT
Ignition on, engine not running.
With the scan tool, read Engine DTCs.
Are any other transmission DTCs present?
Yes >>Refer to the Transmission category and perform the appropriate symptom(s).
No >>Go To 2
2. CHECK IF THE GOVERNOR PRESSURE IS ABOVE 3 PSI IN DRIVE
CAUTION: Apply the parking brake.
Start the engine and allow the transmission to reach normal operating temperature above 43°C (110°F).
CAUTION: Apply the brakes. With the engine at idle, place the gear selector in Drive. With the scan tool, read the Governor Pressure.
Is the Governor Pressure above 21 kPa (3 psi)?
Yes >>Go To 3
No >>Go To 4
3. CHECK IF THE GOVERNOR PRESSURE IS BELOW 3 PSI
Turn the ignition off to the lock position.
Install a pressure gauge at the Governor Pressure test port.
NOTE: Use the appropriate pressure gauge for the pressure range measured.
CAUTION: Apply the parking brake.
Start the engine and allow the transmission to reach normal operating temperature above 43°C (110°F).
CAUTION: Apply the brakes. With the engine at idle, place the gear selector in Drive. Read the governor pressure on the pressure gauge.
Is the governor pressure on the pressure gauge below 21 kPa (3 psi) with the engine at idle and the gear selector in Drive?
Yes >>The Governor Pressure Solenoid is functioning properly. Go To 7
No >>Go To 10
4. GOVERNOR PRESSURE BETWEEN 40-55 WITH RELAY REMOVED
Place the gear selector in Park. With the engine still running, remove the Transmission Control Relay.
WARNING: Do not wear loose clothing or jewelry when working on or near a running engine. Failure to follow these instructions can result in personal injury or death.
NOTE: Relay removal may set various DTCs. Disregard any DTC that may set due to relay removal.
CAUTION: Apply the brakes.
Place the gear selector in Drive and allow the engine to idle for 30 seconds.
With the scan tool, read the Actual Governor Pressure at idle.
Is the governor pressure on the scan tool between 276 - 379 kPa (40 - 55 psi)?
Yes >>Go To 5
No >>Go To 6
5. GOVERNOR PRESSURE SOLENOID
Turn the ignition off to the lock position.
Replace the Governor Pressure Solenoid per the Service Information.
Start the engine and allow the transmission to reach normal operating temperature above 43°C (110°F).
With the scan tool, monitor the target governor pressure and actual governor pressure.
Drive the vehicle at a constant speed 40 - 48 km/h (25 - 30 MPH).
NOTE: The Actual Governor Pressure should be within 21 kPa (3 psi) of the Target Governor Pressure within 3 seconds.
Is the Actual Governor Pressure within 21 kPa (3 psi) of the Target Governor Pressure?
Yes >>Go To 13
No >>Repair internal transmission leak. Inspect all components pertaining to the Governor Pressure Sensor and the Governor Pressure Solenoid.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
6. CHECK GAUGE PRESSURE 40-55 WITH RELAY OUT
Place the gear selector in Park.
With the engine still running, remove the Transmission Control Relay.
WARNING: Do not wear loose clothing or jewelry when working on or near a running engine. Failure to follow these instructions can result in personal injury or death.
NOTE: Relay removal may set various codes. Disregard any DTC that may set due to relay removal.
CAUTION: Apply the brakes. Place the gear selector in Drive with the engine at idle. Read the governor pressure on the pressure gauge.
Is the governor pressure on the pressure gauge read between 276 - 379 kPa (40 - 55 psi)?
Yes >>Go To 7
No >>Go To 10
7. CHECK THE 5 VOLT SUPPLY CIRCUIT FOR AN OPEN - EXTERNAL
Turn the ignition off to the lock position.
Disconnect the Transmission Solenoid Assembly harness connector.
Disconnect the ECM harness connectors.
NOTE: Check connectors - Clean/repair as necessary
Measure the resistance of the 5-volt Supply circuit between the Transmission Solenoid Assembly harness connector and the ECM C2 harness connector.
Is the resistance below 5.0 ohms?
Yes >>Go To 8
No >>Repair the 5-volt Supply circuit for an open.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
8. CHECK THE 5 VOLT SUPPLY CIRCUIT FOR AN OPEN - INTERNAL
Remove the transmission oil pan.
Reconnect the Transmission Solenoid Assembly harness connector.
Disconnect the Governor Pressure Sensor connector internal to the transmission.
Measure the resistance of the 5-volt Supply circuit between the ECM C2 harness connector and the Governor Pressure sensor connector internal to the transmission.
Is the resistance below 5.0 ohms?
Yes >>Go To 9
No >>Repair or replace the 5-volt Supply circuit for an open internal to the transmission.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
9. GOVERNOR PRESSURE SENSOR
Reconnect the ECM harness connectors.
NOTE: The ECM harness connectors must not be disconnected during this test.
Ignition on, engine not running.
Measure the voltage of the 5-volt Supply circuit at the Governor Pressure Sensor connector internal to the transmission.
Is the voltage between 4.5 and 5.5 volts?
Yes >>Replace the Governor Pressure/Transmission Temperature Sensor per the Service Information.
Perform RF TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>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
10. TRANSMISSION - INTERNAL DAMAGE
Turn the ignition off to the lock position.
Remove the transmission oil pan per the Service Information.
Inspect the transmission oil pan for burnt transmission fluid and/or excessive debris.
Is the transmission fluid burnt and/or contain excessive debris?
Yes >>Repair the internal transmission per the Service Information.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Go To 11
11. CHECK THE VALVE BODY
Replace the Governor Pressure Solenoid per the Service Information.
Install a pressure gauge at the governor pressure test port.
Start the engine.
Warm the transmission to normal operating temperature.
CAUTION: Apply the brakes. Place the gear selector in Drive and allow the engine to idle. Read the governor pressure on the pressure gauge in Drive.
Is the governor pressure on the gauge below 21 kPa (3 psi)?
Yes >>Go To 12
No >>Repair or replace the Valve Body per the Service Information.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
12. VERIFY OPERATION - TEST DRIVE
Remove the pressure gauge from the transmission.
Test drive the vehicle.
Be sure to drive the vehicle at a constant speed of 40-48 km/h or 25-30 MPH during the drive cycle. With the scan tool, read Engine DTCs.
Did 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
13. INTERMITTENT WIRING AND CONNECTORS
The conditions necessary set this DTC are not present at this time.
Use the Freeze Frame Data to help duplicate the conditions that set the DTC. Pay particular attention to the DTC set conditions, such as, VSS, MAP, ECT, and Load.
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.
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.