P0128

P0128-THERMOSTAT RATIONALITY

For a complete wiring diagram refer to the Wiring Information Electrical Diagrams. Electrical Diagrams

- When Monitored:
While the engine is running.

- Set Condition:
The coolant temperature does not rise by a calibrated amount over a calibrated amount of time.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure

1. COOLANT LEVEL

NOTE: An engine block heater or oil heater can cause this DTC to set erroneously.

1. Turn the ignition off.
2. With the engine cold, verify the level of coolant in the cooling system.

Is the cooling system full of coolant?

Yes

- Go To 2

No

- Fill the cooling system to the proper level.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

2. COOLANT TEMPERATURE SENSOR
1. Start the engine.
2. With the scan tool, monitor the coolant temperature for 10 minutes.

Did the coolant temperature change over time while the engine was running?

Yes

- Replace the thermostat.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

No

- Replace the Coolant Temperature Sensor.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test