Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit Description
Engine Coolant Temperature (ECT) sensor is a thermistor located in lower coolant passage in cylinder head. ECT sensor resistance is high when coolant temperature is cold and resistance drops when coolant temperature increases. PCM provides a 5-volt reference and a ground signal to ECT sensor. PCM reads voltage drop on the signal line to determine coolant temperature. ECT sensor is used for fuel/ignition control, hot/cold coolant light, temperature gauge and cooling fan.
DTC P0118 will set if ECT reads less than -31°F (-35°C) when engine has been running for more than 4 minutes. ECT signal is continuously monitored when ignition is on.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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