Engine Coolant Temperature (ECT) Sensor

On Cherokee and Wrangler, ECT sensor is installed into the thermostat housing. On Grand Cherokee, ECT sensor is mounted on top of engine, next to thermostat housing. It provides a variable signal to the PCM that is used to calculate injector pulse width and ignition timing. When engine is cold, PCM will operate engine in an open loop cycle, causing slightly higher air/fuel mixture and higher idle speeds. When normal operating temperatures are reached, PCM will operate engine in a closed loop cycle.