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
The DTC P0116 Engine Coolant Temperature (ECT) sensor performance diagnostic monitors ECT sensor activity. ECT sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. ECT sensors resistance is high when coolant temperature is cold, and ECT sensors resistance is low when coolant temperature is warm. ECT sensor is wired in series with a fixed resistor in the Powertrain Control Module (PCM). PCM applies 5 volts to ECT sensor. PCM monitors voltage across ECT sensor and converts voltage into a temperature reading. PCM will receive a high voltage input when coolant temperature is cold. PCM will receive a low voltage input when coolant temperature is warm. A DTC P0116 may set if the ECT sensor voltage does not indicate engine coolant temperature has increased sufficiently during engine operation. See TEMPERATURE VS. RESISTANCE table.
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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.