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
The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit.
The PCM uses this high side coolant rationality diagnostic, to determine if the input from the ECT sensor is skewed high. The internal clock of the PCM will record the amount of time the ignition is OFF. If the calibrated ignition OFF time is met at start-up, then the PCM will compare the temperature difference between the ECT and the Intake Air Temperature (IAT), to determine if the temperatures are within an acceptable operating range of each other.
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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.