Engine Coolant Temperature Signal Invalid
The engine control module has detected an invalid reading from the coolant temperature sensor.
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What it means (plain English)
The coolant temperature sensor reports the engine's temperature to the computer. If the signal is too high or too low, the computer thinks something's wrong, which can affect performance and emissions.
What the computer is actually seeing
The engine control module (ECM) expects to see a voltage from the coolant temperature sensor between 0.5V and 4.5V, corresponding to a temperature range of about -40°C to 125°C (-40°F to 257°F). If the sensor reports values outside this range, it triggers the fault.
What a healthy reading looks like
Coolant temperature should typically be between 85°C (185°F) and 105°C (221°F) when the engine is running normally. The sensor should output 0.5V at -40°C and 4.5V at 125°C.
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 wiring and connector to the coolant temperature sensor for any damage or corrosion. Repair as necessary.
- 22. Using a multimeter, measure the voltage at the connector with the engine running. Expect 0.5V to 4.5V based on temperature; if outside this range, note the actual voltage reading.
- 33. If voltage is out of range, replace the coolant temperature sensor and recheck codes after clearing them.
- 44. If voltage is normal, check the wiring for shorts or opens back to the ECM.
- 55. Inspect the ECM for any internal faults if wiring checks good and sensor is new.
Common causes
- Faulty coolant temperature sensor
- Damaged wiring or poor connections to the sensor
- ECT signal shorted to voltage or ground
- Temperature gauge malfunction leading to wrong readings
Typical repair cost
$$-$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally drivable but it could affect engine performance and fuel economy. Fix soon.
Will this code come back after clearing?
If the underlying issue is not resolved, yes, it likely will return.
Why do I see this code paired with others?
Faults in one sensor often affect others, causing multiple codes to trigger.
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