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/System Description: P0116
The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The control module supplies 5 volts to the signal circuit and a ground for the ECT low reference circuit. When the ECT is low, the sensor resistance is high. When the ECT is high, the sensor resistance is low. The control module uses this High Side Coolant Rationality test to determine if the ECT input is skewed high. The internal clock of the control module will record the amount of time the ignition is OFF. At restart, the control module will compare the temperature difference between the ECT and the intake air temperature (IAT). Before failing this test, the control module will perform a calculation to determine the presence of an engine block heater. If the control module detects that the temperature difference between the ECT and the IAT is not within the calibrated range after the ignition OFF time, DTC P0116 sets.
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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.