P0128

P0128-THERMOSTAT RATIONALITY

For complete wiring diagrams refer to Diagrams/Electrical.


- 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.

Diagnostic Test


1. COOLING FAN

NOTE: Refer to the no trouble code test Fan Operation Test to ensure the fan is operating properly.

Is the cooling fan operating properly?

Yes

- Go To2

No

- Repair the cooling fan.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. COOLANT TEMPERATURE SENSOR

Operate the engine for 10 minutes while monitoring the coolant temperature with the scan tool.

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

Yes

- Go To3

No

- Replace the coolant temperature sensor.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

3. THERMOSTAT

NOTE: Refer to the no trouble code test Thermostat Test to ensure the thermostat is operating properly.

Is the thermostat operating properly?

Yes

- Test Complete.

No

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