Electric Cooling Fan Diagnosis

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The auxiliary cooling fan is controlled by the Vehicle Control Module (VCM) based on various inputs. Battery voltage is supplied to the auxiliary cooling fan relay. ignition voltage is supplied to the auxiliary fan relay (coil side). The VCM controls the cooling fan relay by providing a ground path.

Diagnostic Aids

If the driver complaint is an overheating problem, it must be determined if the complaint was due to an actual boil over, or the warning indicator light, or engine coolant temperature gage indicated overheating. The gage accuracy can also be checked by comparing the Engine Coolant Temperature (ECT) sensor reading using a scan tool and comparing its reading with the gage reading. If the engine is actually overheating and the gage indicated overheating, but the cooling fan is not coming ON, the Engine Coolant Temperature (ECT) sensor has probably shifted out of calibration and should be replaced.

If the engine is overheating and the cooling fan is ON, the cooling system should be checked, refer to Engine, Cooling and Radiator.

The VCM will command the auxiliary cooling fan on at 107°C (225°F) and OFF at 103°C (218°F).

Test Description

Number(s) below refer to step numbers on the diagnostic table.

3. Engine coolant temperature must be below 100°C (212°F) to perform this test.

8. This check can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm the coil may open (amps drop to 0), or short (goes above 0.75 amp).

12. Listen for an audible click when the relay operates. Be sure that both the ON and OFF states are commanded. Repeat the commands as necessary.

24. If no trouble is found in the control circuit or the connection at the VCM, the VCM may be faulty, however, this is an extremely unlikely failure.