P0118 - Engine Coolant Temperature Circuit High Input
P0118 means the coolant temperature signal is reading colder than expected because the circuit is open or the signal is stuck high. It is not automatically just a bad coolant temperature sensor; an unplugged sensor, damaged wiring, connector corrosion, open circuit, failed sensor, or less common PCM and reference-voltage issue can set the same code.
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Code Overview
P0118 means the coolant temperature signal is reading colder than expected because the circuit is open or the signal is stuck high. It is not automatically just a bad coolant temperature sensor; an unplugged sensor, damaged wiring, connector corrosion, open circuit, failed sensor, or less common PCM and reference-voltage issue can set the same code.
Common Causes
- Unplugged coolant temperature sensor
- Open circuit or broken wiring in the ECT sensor path
- Failed engine coolant temperature sensor
- Coolant intrusion or corrosion at the connector
Symptoms
- Hard cold starts or rich-running behavior
- Cooling-fan operation may be abnormal
- Fuel economy can drop while warm-up strategy stays on too long
Diagnostic Steps
- Make sure the coolant temperature sensor connector is fully seated
- Inspect the wiring for breaks, corrosion, or coolant intrusion
- Compare ECT reading to ambient temperature on a cold engine
- Check sensor resistance and circuit integrity before replacing parts
Diagnostic Insight
P0118 should be treated as a coolant-temperature circuit-high fault before the sensor itself is condemned.
- A cold-looking ECT reading on a warm engine often points to an open circuit or poor connection.
- Connector corrosion, coolant intrusion, or broken wiring can mimic a failed sensor.
- Cold-engine scan data should be compared to ambient temperature before parts are replaced.
Repair Difficulty
Easy
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