Engine Coolant Temperature Sensor (ECT)
Coolant temperature sensor signal out of range.
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What it means (plain English)
The engine coolant temperature sensor measures how hot the coolant is. If it sends a signal that is too high or too low, the engine control module gets confused and triggers a fault code.
What the computer is actually seeing
The ECM expects the coolant temperature to be between 180°F and 220°F. If it sees a signal below -40°F or above 275°F, it triggers the code.
What a healthy reading looks like
Expected values for the ECT sensor are between 0.5V (approximately -40°F) and 4.5V (approximately 275°F). Normal operating range is roughly 0.7V to 3.5V for typical running temperatures.
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 coolant level and add if low; if low, top off and retest.
- 2Inspect wiring and connectors to the ECT sensor for damage or corrosion; repair as necessary.
- 3Measure the voltage at the ECT sensor connector. You should see a voltage correlated to temperature (0.5V to 4.5V). If the voltage is out of this range, sensor may need replacing.
- 4Monitor the coolant temperature using a scan tool or multimeter while the engine warms up. If readings are not changing with engine temperature, replace the ECT sensor.
Common causes
- Faulty coolant temperature sensor
- Wiring issues or bad connector
- Corroded or damaged sensor
- Air pockets in the cooling system
Typical repair cost
$$$ (typically $200-$350)
Related codes
Frequently asked questions
Is it safe to drive with this code?
Yes, but monitor engine temperature closely to prevent overheating.
Will the code come back after repairs?
If the cause is fixed, it should not return. Clear the code and monitor.
Why does it pair with SPN 0590?
SPN 0590 relates to the ECT sensor signal, so they often trigger together when there's an issue with the sensor or circuit.
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