Engine Coolant Temperature - High
The engine coolant temperature is too high.
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What it means (plain English)
The engine computer is reading the coolant temperature as being hotter than normal, indicating possible overheating.
What the computer is actually seeing
The engine control module (ECM) expects coolant temperatures between 180°F to 220°F (82°C to 104°C) during normal operation. If it sees temperatures above 240°F (116°C), it triggers the fault code.
What a healthy reading looks like
Coolant Temperature: 180°F to 220°F (82°C to 104°C) during normal operation; over 240°F (116°C) triggers code.
Guided diagnostic — the DiagCoach way
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.
- 11. Check coolant level in the reservoir. Is it low? If yes, fill it to the proper level and retest.
- 22. Inspect for any leaks around hoses and the radiator. Are there visible leaks? If yes, repair them, refill coolant, and retest.
- 33. Use a scan tool to check the actual coolant temperature reading. Is the sensor reading above 240°F (116°C)? If yes, continue to the next step.
- 44. Disconnect the coolant temperature sensor connector. Measure resistance with a multimeter. Is it out of spec (faulty sensor)? If yes, replace the sensor.
- 55. Check the thermostat by removing it and testing in hot water. Does it open at its specified temperature (typically around 195°F or 90°C)? If no, replace the thermostat. If yes, continue to next step.
- 66. Inspect the water pump function. Is it working properly (circulating coolant)? If no, replace the water pump.
Common causes
- Low coolant level
- Faulty coolant temperature sensor
- Stuck thermostat
- Cooling system blockage
- Worn water pump
Typical repair cost
$$-$$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
No, driving with high coolant temperature can cause engine damage. Stop the vehicle and check the cooling system.
Will this code come back after repairs?
If repaired correctly, this code should not return. However, monitor for any recurring issues in the cooling system.
Why is this code paired with SPN 1009?
SPN 1009 relates to coolant temperature reservoir sensor. If coolant levels are low, both codes can appear due to similar causes.
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