P0118
OBD-II Diagnostic Code
Severity: ModerateWhat Does This Error Mean?
P0118 means the engine coolant temperature (ECT) sensor is sending an abnormally high voltage signal. This usually means the sensor or its wiring has failed — not that the engine is actually overheating. Check the sensor connector and wiring first.
Affected Models
- All OBD-II vehicles (1996+)
Common Causes
- ECT sensor failed (open circuit)
- Wiring to sensor disconnected or broken
- Corroded sensor connector
- Faulty ECM reading
- Actual engine overheating (less common cause of this code)
How to Fix It
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Check the ECT sensor connector for corrosion or disconnection.
The sensor is usually near the thermostat housing. Unplug and inspect the connector for green corrosion or bent pins.
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Test the sensor resistance with a multimeter.
A cold sensor should read 2,000-3,000 ohms. A hot sensor reads 200-300 ohms. Infinite resistance (open circuit) means the sensor is bad.
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Replace the ECT sensor — it is inexpensive and easy to change.
ECT sensors cost $10-$30 and are usually a simple screw-in replacement.
Frequently Asked Questions
Will P0118 cause my engine to overheat?
P0118 itself does not cause overheating — it means the sensor reading is wrong. But if the ECM gets incorrect temperature data, the cooling fan may not activate when needed.
How much does an ECT sensor cost?
The sensor itself costs $10-$30. Labor is usually $50-$100. It is one of the cheapest engine sensors to replace.