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.
DTC P0118: Engine Coolant Temperature Circuit High Input: General Description
The ECTS (Engine Coolant Temperature Sensor) measures the temperature of engine coolant. The ECTS (Engine Coolant Temperature Sensor) is located near the thermostat housing of the cylinder head. The ECTS is a thermistor (A Variable Resistor that changes along with ECT) in series with a fixed resistor in the ECM. The ECM applies 5 volts to the ECTS. The ECM monitors the voltage across the ECTS and converts it into a temperature reading. When the engine is cold the ECTS resistance is high, and when the engine is warm the ECTS resistance is low. Therefore, when the engine is cold the ECM will receive a high voltage input, and when the engine is warm the ECM will receive a low voltage input. The signal from the ECTS is used for Injection control, ignition timing, idle speed and cooling fan control.
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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.