Engine Coolant Temperature
Indicates an issue with the engine coolant temperature sensor or circuit.
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What it means (plain English)
The engine coolant temperature sensor tracks how hot the engine is running. If it fails, the computer doesn’t know if it’s overheating or running too cool, which can cause performance problems.
What the computer is actually seeing
The engine control unit (ECU) monitors the voltage signal from the coolant temperature sensor, which should vary between 0.5 volts (cold) and 4.5 volts (hot).
What a healthy reading looks like
The expected voltage should be between 0.5V and 4.5V, correlating with coolant temperatures from around 0°C to 100°C (32°F to 212°F).
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 the coolant level; it should be between the minimum and maximum marks. If low, top it up and see if the code returns.
- 22. Inspect the wiring and connector at the coolant temperature sensor for damage or corrosion. Repair as necessary.
- 33. Using a scan tool, observe the coolant temperature reading at startup. It should closely match the ambient temperature. If not, suspect sensor failure.
- 44. Measure the voltage at the coolant temperature sensor output while the engine is running. Ensure it varies between 0.5V and 4.5V as the engine warms up.
- 55. If the readings are outside normal values, replace the coolant temperature sensor and clear the code.
Common causes
- Failed coolant temperature sensor
- Open or shorted wiring to the sensor
- Low coolant level
- Faulty ECU
Typical repair cost
$$
Related codes
Frequently asked questions
Can I still drive the vehicle with this code?
Yes, but expect poor performance and possible overheating.
Will the problem return after fixing?
If the sensor or wiring was faulty and replaced correctly, it should not return.
Why is this code paired with engine performance issues?
An inaccurate coolant temperature reading can lead to incorrect fuel mapping and timing adjustments.
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