Engine Coolant Temperature Sensor
Indicates a problem with the engine coolant temperature sensor signal.
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What it means (plain English)
The engine coolant temperature sensor measures the coolant temperature, helping the computer adjust fuel mixture and timing. If this sensor fails, the computer may not get accurate temperature readings, causing performance issues.
What the computer is actually seeing
The engine control module (ECM) expects a varying voltage signal from the coolant temperature sensor that ranges from 0.5V (cold engine) to 4.5V (hot engine).
What a healthy reading looks like
0.5V at 32°F, up to 4.5V at 248°F; Expected resistance should change from 2500 ohms (32°F) to 200 ohms (212°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 wiring and connectors at the coolant temperature sensor. Look for signs of damage or corrosion. If wiring is good, revisit your connections.
- 22. Ensure coolant level is proper; if low, top it off and see if code returns after a short test drive.
- 33. Test the coolant temperature sensor with a multimeter. At a cold start (32°F), you should read 2500 ohms and at 212°F, it should drop to 200 ohms. If it's out of range, replace the sensor.
- 44. Clear the code and take the vehicle for a test drive to see if the code returns. If it does, further investigation into the ECM or wiring may be necessary.
Common causes
- Faulty coolant temperature sensor
- Wiring issues (fraying, corrosion, shorts)
- Poor connector contact
- Coolant leaks affecting temperature readings
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's best to fix it soon; the engine may run poorly or overheat.
Will this code come back after clearing?
Yes, if the sensor is faulty or there's a wiring issue, it will likely return.
Why does this code appear with SPN 100?
SPN 100 (Engine Coolant Temperature) could be confirming the same issue with the temperature readings.
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