Coolant Temperature Sensor Voltage High
Indicates a high voltage reading from the coolant temperature sensor.
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What it means (plain English)
The engine's computer is seeing a voltage from the coolant temp sensor that’s too high, which means it thinks the engine is running hotter than it actually is, potentially leading to overheating issues.
What the computer is actually seeing
The engine control module (ECM) expects a voltage signal between 0.5V and 4.5V from the coolant temperature sensor. If the voltage exceeds 4.5V, this code triggers.
What a healthy reading looks like
Normal coolant temperature sensor output should be between 0.5V (cold) to 4.5V (hot) at operating temperatures.
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 damage or corrosion. Is everything intact? If no, repair the wiring. If yes, proceed.
- 22. Measure the voltage at the coolant temperature sensor connector. What reading do you get? If over 4.5V, replace the coolant temperature sensor. If under 4.5V, proceed.
- 33. Check for any recent modifications or repairs in the cooling system. Has anything been changed? If yes, double-check those repairs. If no, proceed.
- 44. If everything else checks out, re-scan the system after clearing the code. Does the code return? If yes, consider testing or replacing the ECM.
Common causes
- Shorted coolant temperature sensor
- Damaged wiring to the sensor
- Faulty engine control module (ECM)
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not advisable to drive long distances, as it could lead to engine overheating.
Will this code come back after I clear it?
If the underlying issue isn’t fixed, yes, it will likely return.
Why is this code appearing along with SPN 0278?
SPN 0278 indicates a fault with the intake air temperature sensor, which can sometimes trigger multiple codes if the engine is experiencing temperature misreads.
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