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:

^ The A/C is "ON."
^ The coolant temperature is greater than 105°C (221°F).
^ Code 14 coolant sensor failure.

DIAGNOSTIC AIDS

^ 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 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 also be checked by comparing the coolant sensor reading using a Scan tool and comparing its reading with the gauge reading.
^ 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.