Engine Coolant Temperature Sensor 1 Out of Range
The engine coolant temperature sensor is reporting a temperature that is out of the expected range.
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What it means (plain English)
The engine coolant temperature sensor tracks how hot the engine coolant is. If it reports a temperature that's too high or low (like below -40°F or above 257°F), the computer thinks there's a problem and triggers a code.
What the computer is actually seeing
The Electronic Control Unit (ECU) sees voltage signals from the coolant temperature sensor. These signals should typically be between 0.5 volts (cold engine) and 4.5 volts (hot engine). If the voltage is outside this range, the ECU registers a fault.
What a healthy reading looks like
Normal operating temperature should be around 195°F to 220°F, translating to roughly 1.0V to 2.5V from the sensor signal.
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 coolant level and top off if low, then clear the code and test drive the vehicle. If the code returns, proceed to step 2.
- 22. Inspect the wiring and connectors at the coolant temperature sensor for damage or corrosion. Repair as needed and retest.
- 33. Measure the voltage at the coolant temperature sensor with the engine running. Values outside 0.5V to 4.5V need investigation into the sensor and wiring. If normal, check the ECU.
- 44. If the sensor's voltage is out of range, replace the coolant temperature sensor and retest.
- 55. If issues persist after the sensor replacement, diagnose the ECU for faults.
Common causes
- Faulty engine coolant temperature sensor
- Wiring issues (shorts or opens) in the circuit
- Poor connection at the sensor or ECU
- Low coolant level
- Coolant leaks affecting sensor readings
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally safe but can lead to engine overheating or poor performance if not addressed.
Will this code come back after clearing?
It may return if the underlying issue (sensor or wiring) isn’t fixed.
Why does this code pair with SPN 1502?
SPN 1501 indicates a sensor reading issue, while SPN 1502 can signify a different sensor or circuit problem that could affect the same system.
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