For 1990-2009 cars

When the ignition switch is in the ON position, system voltage is applied through the IG-COIL fuse (in the junction block) to the engine cooling fan relay (RDTR). The Powertrain Control Module (PCM) will apply ground to the coil side of the engine cooling fan relay (RDTR) when the PCM senses high engine coolant temperature 98°C (208°F) from the engine coolant temperature (ECT) sensor. With power and ground applied to the coil of the engine cooling fan relay (RDTR), the contacts close and voltage is applied through the RDTR fuse to the engine cooling fan motor. The engine cooling fan motor is permanently grounded at G102 and will continue to operate until the engine coolant temperature falls below 93°C (199°F).

When the engine coolant temperature falls below 93°C (199°F), the PCM will interrupt ground to the coil side of the engine cooling fan relay (RDTR), the contacts open and the engine cooling fan motor stops.