Engine Coolant Temperature Sensor 1
Indicates an issue with the engine coolant temperature sensor signal.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine coolant temperature sensor tells the computer how hot the engine coolant is, usually running between 185°F to 220°F when the engine is warm. If it's reading too high or too low, the computer can get confused and cause performance issues.
What the computer is actually seeing
The engine control module (ECM) expects to see a signal voltage from the coolant temperature sensor ranging from about 0.5V (for -40°F) to 4.5V (for 250°F). A reading outside this range or no signal can trigger this code.
What a healthy reading looks like
Expected voltage is between 0.5V and 4.5V, with normal operational range around 0.9V to 1.5V when the engine is cold and 2.5V to 3.5V when operating normally.
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.
- 1Check the engine coolant level—add coolant if low.
- 2Inspect the wiring and connector for damage—look for frays or corrosion.
- 3Using a multimeter, check the voltage at the coolant temperature sensor connector—it should read within expected values.
- 4If readings are out of range, replace the coolant temperature sensor and retest. If normal, check the ECM for faults.
Common causes
- Faulty engine coolant temperature sensor
- Wiring issues or short circuits
- Connector problems or corrosion
- Coolant level too low
- ECM malfunction
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's best to fix it soon as it can affect engine performance, but you may be able to drive for a short time.
Will this code come back after clearing?
If the underlying issue is not fixed, expect the code to return.
Why does this code sometimes appear with SPN 1251?
SPN 1251 also relates to coolant temperature, indicating possible sensor errors or wiring issues.
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