Engine Coolant Temperature Sensor 1
Indicates a failure in the engine coolant temperature sensor or circuit.
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What it means (plain English)
The engine control module (ECM) isn't getting a proper signal from the coolant temperature sensor, which tells it how hot the engine is running.
What the computer is actually seeing
The ECM expects a voltage between 0.5V to 1.5V when the engine is at normal operating temperature (around 190°F to 220°F).
What a healthy reading looks like
Normal values from the coolant temperature sensor should be 0.5V to 4.5V under operating conditions, corresponding to temperatures from -40°F to 248°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 engine coolant level; ensure it’s at the proper level. Decision: If low, refill and monitor.
- 22. Visually inspect the wiring and connector at the coolant temperature sensor. Look for damage or corrosion. Decision: If damaged, repair or replace wiring/connector.
- 33. Use a multimeter to test the coolant temperature sensor's resistance. At 200°F, it should read approximately 2,000 to 3,000 ohms. Decision: If outside this range, replace the sensor.
- 44. Check the voltage output of the sensor with the engine running. Expected should be between 0.5V and 4.5V. Decision: If voltage is out of this range, wiring issues may be present, otherwise replace the ECM.
Common causes
- Faulty engine coolant temperature sensor
- Wiring issues or short circuits in the sensor circuit
- Corrosion or poor connection at the sensor connector
- Coolant leaks affecting sensor operation
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally drivable, but the engine may not operate efficiently, and could overheat.
Will this issue come back after clearing the code?
If the underlying issue isn't fixed, expect the code to return.
Why does this code sometimes pair with other SPN codes?
Multiple sensor issues or wiring faults can trigger several codes at once.
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