Engine Coolant Temperature Sensor 1
Indicates a problem with the engine coolant temperature sensor reading.
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What it means (plain English)
The engine coolant temperature sensor measures how hot the engine coolant is. If it reads outside the expected range, the engine control module (ECM) thinks the engine isn't at the right temperature for optimal operation.
What the computer is actually seeing
The ECM expects the coolant temperature to be between 190°F (88°C) and 220°F (104°C) during normal operation. If it sees a value below 160°F (71°C) or above 240°F (116°C), it triggers this code.
What a healthy reading looks like
Expected coolant temperature is generally between 190°F (88°C) and 220°F (104°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 engine coolant level; ensure it's within the safe range. If it's low, refill and retest. Decision: If the code returns, proceed to step 2. If no code, problem fixed.
- 22. Inspect the wiring and connector for the coolant temperature sensor for any signs of damage or corrosion. Repair any identified issues. Decision: If the code returns, proceed to step 3. If no code, problem fixed.
- 33. Measure the voltage at the engine coolant temperature sensor connector with the engine running. You should see about 0.5V at cold and up to 4.5V when hot. Decision: If readings are out of range, replace the sensor. If readings are normal, problem lies elsewhere.
Common causes
- Faulty engine coolant temperature sensor
- Wiring issue between the sensor and the ECM
- Coolant leaks or low coolant level
- Faulty engine thermostat
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's best to address this code soon, as it can affect engine performance and emissions, but short trips may be okay if the vehicle isn't overheating.
Will the code come back after clearing it?
If the underlying issue isn't fixed, yes, it likely will return.
Why do I sometimes see this paired with other codes?
The engine coolant temperature affects many systems, so issues there can relate to various components.
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