Chart C-12 Coolant Fan Control Circuit

Chart C-12:

Wiring Diagram For Cooling Fan:

CIRCUIT DESCRIPTION:

Battery voltage is supplied to terminal "1" in order operate the cooling fan motor. Terminal "5" of the relay has ignition voltage supplied to it. When the ECM grounds circuit 335, the relay and the cooling fan are energized. When the engine is running, the ECM will energize the cooling fan if a Coolant Temperature Sensor (CTS) code is set, or if the following conditions exist.

1. The A/C is ON and the vehicle speed is less than 30 mph (48 km/h).
2. The coolant temperature is greater than 108~C (230~F).


DIAGNOSTIC AIDS:

1. If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over, the temperature light, or the temperature gauge indicates overheating.
2. If the gauge or light indicates overheating, but no boil over is detected, the gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using a Scan tool and comparing its reading with the gauge reading.
3. If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not energized, the coolant sensor has probably shifted out of calibration and should be replaced.
4. If the engine is overheating, and the cooling fan is running, the cooling system should be checked.