High Engine Coolant Temperature

The engine is getting too hot, which can cause serious damage if it runs like this for too long. The computer keeps track of the coolant temperature via a sensor; if it gets over a set limit, the engine can go into protective mode.

The engine control module (ECM) monitors the coolant temperature sensor (CTS) input voltage. A high temperature signal might show a voltage above 4.5 volts, indicating overheating.

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 in the reservoir and radiator; top off if low. Decision: If coolant is low, refill and run the engine. If not, proceed to step 2.
2. 22. Inspect for visible coolant leaks around hoses, engine block, and the radiator. Decision: If leaks are found, repair the leaks and refill coolant. If no leaks, proceed to step 3.
3. 33. Test the coolant temperature sensor with a multimeter; expect around 2.5V to 4.2V at normal operating temperature (200°F / 93°C). Decision: If it's outside this range, replace the sensor. If within range, proceed to step 4.
4. 44. Check the thermostat operation; run the engine until it reaches operating temperature and feel for warmth in the upper radiator hose. Decision: If the hose is cold, replace the thermostat. If it warms up, check the operation of the radiator fan. Proceed to step 5.
5. 55. Verify the radiator fan operation by using a scan tool or direct power. Decision: If the fan does not engage, test the fan relay and circuit. If fan is operational, check for possible engine mechanical issues.

• Low coolant level
• Faulty coolant temperature sensor
• Cooling system leaks
• Thermostat stuck closed
• Inoperative radiator fan

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