Engine Coolant Temperature Sensor 1 - Out of Range
The coolant temperature sensor is reporting a value that the ECM considers too high or too low.
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What it means (plain English)
The computer is getting a coolant temperature reading that doesn’t make sense—either way too hot (above 250°F/121°C) or way too cold (below 32°F/0°C).
What the computer is actually seeing
The ECM expects the coolant temperature to be between 160°F (71°C) and 220°F (104°C) under normal operating conditions. If it sees values consistently outside this range, it triggers the fault.
What a healthy reading looks like
Normal operation: 160°F (71°C) to 220°F (104°C); Fault triggered below 32°F (0°C) or above 250°F (121°C).
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 for corrosion, fraying, or disconnection. Repair any issues found.
- 22. Verify the coolant level in the reservoir; add coolant if low. Check for leaks. If the system is low on coolant, that could affect the sensor's accuracy.
- 33. Using a scan tool, check the coolant temperature reading. If it's below 32°F (0°C) or above 250°F (121°C), proceed to the next step.
- 44. Measure the resistance of the coolant temperature sensor using a multimeter. At 68°F (20°C), the resistance should be around 2,200 ohms. If it's outside this range, replace the sensor.
- 55. If the sensor checks out, inspect the coolant temperature sensor wiring for shorts or opens back to the ECM.
Common causes
- Faulty coolant temperature sensor
- Open or short circuit in the sensor wiring
- Corroded or loose connector at the sensor
- Cooling system low on coolant or air in the system
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with SPN 1042?
It's typically drivable, but some cooling issues can lead to overheating, risking engine damage.
Will this code come back after clearing?
If the issue isn't fixed, yes, it will likely return.
Why does this code show up with other codes?
Related codes often indicate issues in the same system—for example, other sensors or cooling system performance.
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