P0118 – Engine Coolant Temperature Circuit High Input

Description

The ECM detects an abnormally high voltage from the ECT sensor, usually caused by an open circuit or sensor failure.

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Symptoms

Check engine light
Poor fuel economy
Hard starting
Cooling fans always on
High idle

Causes

Open circuit in ECT wiring
Faulty ECT sensor
Corroded connector
Low coolant
ECM fault

Diagnosis

Monitor ECT voltage
Inspect wiring for opens
Check coolant level
Compare sensor reading to actual temp

Repair

Replace ECT sensor
Repair wiring
Fix connector
Refill coolant
Replace ECM if required