Diagnostic Aids
Perform this test when directed by QUICK TEST. This test is intended to diagnose the following:
- Engine Coolant Temperature (ECT) Sensor
- Wiring Harness Circuits (ECT & SIG RTN)
- Powertrain Control Module (PCM)
The Engine Coolant Temperature (ECT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature. The engine coolant sensor is used as the primary input to the electronic control system to enable adaptive cooling. This provides a means of providing adequate cooling in severe engine temperature conditions. When the ECT is greater than 22°F (10°C), the fueling rate of the engine is modified to provide cooling protection and prevent engine damage due to overheating.
The ECT sensor is located on the left side of the front cover. The PCM supplies a 5-volt reference signal that the ECT sensor uses to produce an analog voltage, indicating temperature. The PCM continuously monitors the signal of the ECT sensor to determine if the signal is within an expected range. If the PCM detects an out of range high or low, the PCM will ignore the ECT signal and assume an engine coolant temperature of -29°F (-34°C) for starting and 180°F (82°C) for engine running conditions.