High Engine Coolant Temperature

The engine control module (ECM) thinks the engine is overheating, which could cause serious damage if not addressed. It sees a high temperature from the coolant sensor.

The ECM constantly monitors the coolant temperature sensor input. If the temperature reading exceeds the defined threshold (typically over 245°F / 118°C), it triggers the code.

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 coolant level in the reservoir; replenish if low. Decision: Low coolant? If yes, fix leak, if no, proceed to step 2.
2. 22. Inspect wiring and connector at the coolant temperature sensor for damage or corrosion. Decision: Damage found? If yes, repair/replace wiring; if no, proceed to step 3.
3. 33. Use a scan tool to monitor live data from the coolant temperature sensor. Compare with ambient temperature; expect readings within 5°F of actual ambient. Decision: Sensor reading accurate? If not, replace coolant temperature sensor; if yes, proceed to step 4.
4. 44. Check for external issues such as blocked radiator or issues with airflow. Inspect for debris and clear as needed. Decision: Blockage found? If yes, clean or replace radiator; if no, proceed to step 5.
5. 55. Conduct a visual inspection of the thermostat and water pump for functionality. Decision: Any component malfunction? If yes, replace defective part; if no, consult further engine diagnostics.

• Coolant leak
• Faulty coolant temperature sensor
• Blocked radiator
• Failed thermostat
• Water pump failure

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