Coolant Temperature Sensor 1 - Out of Range
The engine control module (ECM) detects an abnormal coolant temperature reading.
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What it means (plain English)
The coolant temperature sensor is reporting a temperature that's too high or too low, which doesn’t match the operating conditions of the engine. For example, it may indicate -40°F when the engine is actually warming up, or over 250°F when the engine is cooling down.
What the computer is actually seeing
The ECM expects to see a coolant temperature in a specific range. Typically, this is around 190°F to 220°F when the engine is at normal operating temperature. If the sensor gives a reading outside of the normal range, the ECM triggers the SPN 3815 code.
What a healthy reading looks like
Normal coolant temperature readings should be between 190°F and 220°F (88°C - 104°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.
- 1Check the coolant level in the reservoir and radiator. Low coolant could cause erroneous readings. If low, top off and recheck codes after engine runs.
- 2Inspect the wiring and connectors at the coolant temperature sensor for damage or corrosion. Repair if necessary.
- 3Measure the resistance of the coolant temperature sensor at various temperatures to verify its functionality. Use a multimeter and compare the readings to manufacturer specifications. If out of spec, replace the sensor.
- 4Perform a temperature check of the engine with an infrared thermometer. Compare this reading with the coolant temperature reading from the ECM. If they differ significantly, consider replacing the sensor.
Common causes
- Faulty coolant temperature sensor
- Wiring or connector issues
- Low coolant level
- Faulty engine thermostat
- Incorrect ECM calibration
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
While the vehicle might still be drivable, it’s advisable to fix the coolant temperature sensor issue soon to avoid overheating or further damage.
Will this code come back after I clear it?
If the underlying issue isn't resolved, such as a faulty sensor or wiring problem, the code will likely return after clearing.
Why does this code pair with others?
Coolant temperature issues often affect engine performance, which can trigger multiple related codes, especially for sensors impacted by temperature changes.
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