Circuit Description

Engine Coolant Temperature (ECT) sensor is a thermistor in series with a fixed resistor in PCM. PCM applies 5 volts to ECT sensor. PCM monitors voltage across ECT sensor and converts it into a temperature reading. When coolant temperature is cold, ECT sensor resistance is high (PCM monitors high voltage input). When coolant temperature is warm, ECT sensor resistance is low (PCM monitors low voltage input).

DTC will set when engine has been running for at least 20 minutes and vehicle has been driven at speeds of 30 MPH or greater at least once since engine start, and engine coolant temperature (as indicated by ECT sensor) variation is less than expected value.