SENSOR #1 COOLANT TEMPERATURE - ABNORMAL READING
Indicates an abnormal reading from coolant temperature sensor #1.
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What it means (plain English)
The engine control unit is getting a weird or faulty signal from the coolant temperature sensor, making it think the engine's temperature is outside normal range.
What the computer is actually seeing
The ECM is receiving a voltage signal between 0.5V (cold) and 4.5V (hot) from the coolant temperature sensor. An abnormal reading would be below 0.2V or above 4.8V.
What a healthy reading looks like
Expect coolant temp readings between 180°F to 220°F (82°C to 104°C) during normal operation.
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 for damage or corrosion. Repair as needed. Decision: Do connections look good? Yes - go to step 2. No - repair wiring/connectors and retest.
- 22. Measure the voltage at the coolant temperature sensor connector with the engine running. Expected range is between 0.5V and 4.5V. Decision: Is the voltage within range? Yes - sensor is likely functioning normally. No - go to step 3.
- 33. Disconnect the coolant temperature sensor and measure resistance. At 32°F (0°C), resistance should be around 30k ohms; at 212°F (100°C), it should drop to about 300 ohms. Decision: Is the resistance within spec? Yes - go to step 4. No - replace the coolant temperature sensor and retest.
- 44. If the sensor is correct, check for any DTCs in the ECM that may indicate other issues with the engine cooling system. Decision: Are there related codes? Yes - diagnose those codes. No - further investigation needed.
Common causes
- Faulty coolant temperature sensor
- Wiring issues (shorts, opens)
- Connector corrosion or damage
- Coolant leaks affecting sensor operation
Typical repair cost
$$ - $$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate severity; you can drive but should fix soon to avoid overheating or performance issues.
Will this code come back after clearing?
If the underlying issue isn't fixed, yes, the code will likely return.
Why does this code sometimes pair with others?
It's common as multiple sensor malfunctions can affect engine temperature readings.
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