Engine Coolant Temperature - Abnormal Value

The engine computer thinks the coolant temperature isn't normal, which could cause overheating or running too cold.

The Engine Control Unit (ECU) detects that the coolant temperature sensor (CTS) is providing a voltage signal indicating a temperature far outside the normal operating range, usually below 70°C (158°F) or above 120°C (248°F).

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 11. Check the coolant level. Ensure it's at the correct level; it should be between minimum and maximum marks on the reservoir.
2. 22. Inspect the wiring and connectors on the coolant temperature sensor for any visible damage or corrosion. Repair as needed.
3. 33. Use a scan tool to check the current coolant temperature reading from the ECM and compare it to the actual temperature using a separate thermometer. Decision: If the readings differ significantly, the sensor may be faulty.
4. 44. With the engine running, measure the voltage at the coolant temperature sensor connector. Expected voltage should change as the engine warms up, indicating it should be about 0.5V to 4.5V depending on temperature. Decision: If voltage is outside range, replace the sensor.
5. 55. If the sensor is good, check the thermostat operation. Ensure it opens and closes properly. If stuck, replace the thermostat.

• Faulty coolant temperature sensor
• Wiring issues or poor connections in the CTS circuit
• Low coolant level
• Thermostat stuck open or closed
• Engine overheating due to other issues

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