Chart C-12 Coolant Fan Control Circuit

Chart C-12:

Cooling Fan Circuit:

CIRCUIT DESCRIPTION:
Battery voltage to operate the cooling fan motor is supplied to relay by CKT 2. Ignition voltage to energize the relay is supplied to relay by CKT 650. When the ECM grounds CKT 335, the relay is energized and the cooling fan is turned "ON." 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.

^ The A/C is "ON" and the vehicle speed is less than 70 mph (113 km/h) with A/C "OFF."
^ The coolant temperature is greater than 106°C (223°F).

DIAGNOSTIC AIDS:

^ If the vehicle has an overheating problem, it must be determined if the complaint was due to an actual boil over, the coolant temperature warning light, or the temperature gauge indicated overheating.
^ If the gauge or light indicates overheating, but no boil over is detected, the gauge circuit should be checked. The gauge accuracy can be checked by comparing the coolant sensor reading using a "Scan" tool.
^ If the engine is actually overheating, and the gauge indicates overheating, but the cooling fan is not turning "ON," the coolant temperature sensor has probably shifted out of calibration and should be replaced.