Engine Coolant Temperature Below Normal Operating Range

The engine's coolant isn't warming up enough, which can happen if the thermostat is stuck open, there's a coolant leak, or the engine's running too cold for other reasons.

The engine control module (ECM) is looking for a coolant temperature between 180-220°F (82-104°C) once the engine reaches operating conditions, and it sees a temperature under 160°F (71°C) for too long.

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 engine coolant level. If low, refill and recheck for leaks.
2. 22. Inspect the coolant temperature sensor connector for damage or corrosion. Repair if needed.
3. 33. With the engine at operating temperature, check the actual coolant temperature using a scan tool. Is it below 180°F? Yes - proceed to step 4, No - the issue may be elsewhere.
4. 44. Test the coolant temperature sensor resistance at operating temperature. Expected should be around 200-300 ohms. If resistance is too high, replace the sensor.
5. 55. Check the thermostat operation by removing it and placing it in boiling water. It should open fully before water boils. If it sticks or opens late, replace it.

• Stuck open thermostat
• Coolant leak
• Faulty coolant temperature sensor
• Engine running too lean or cold
• Coolant flow issues

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