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

Turn the ignition on.

Using a scan tool, actuate the Condenser Fan

Is the cooling fan operating properly during the actuation?

Yes

- Go To 2

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 To 3

No

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

3. THERMOSTAT

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Start the engine.

Allow the engine to reach normal operating temperature.

Does the thermostat open properly at the correct temperature?

Yes

- Test Complete.

No

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