What is the temperature gauge reading? Normally, the fans do not turn on until the engine reaches over 220 degrees in normal driving conditions. The powertrain control control module (PCM) through output module drivers is what turns the fans on/off by controlling the cooling fan relays. It references to the engine coolant temperature sensor (ECT) to monitor engine temperature by sending a 5v reference signal to the ECT which is a thermal resistor that varies resistance and then sends the varying signal back to the PCM to determine whether fans should be turned on. If you disconnect the ECT the fans should go to the high position.