Chart C-12A Electric Radiator Fan Circuit Diagnosis

Diagnostic Chart:

Electric Radiator Fan Circuit:

CIRCUIT DESCRIPTION
The radiator fan motor is controlled by the Engine Control Module (ECM) through the radiator fan relay. The ECM monitors coolant temperatures through the Engine Coolant Temperature (ECT) sensor. By monitoring the ECT sensor the ECM can calculate when to turn the radiator fan motor "ON," and "OFF" When engine coolant temperatures reach above 95°C (205°F) the ECM will provide a ground path for the radiator fan relay which will turn "ON" the radiator fan motor. When engine coolant temperatures drop below 91°C (197°F) the ECM will remove the ground for the radiator fan relay and the radiator fan motor will be turned "OFF."

CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Checks for proper operation of the radiator fan motor.
2. Checks for an open in the BLU wire between the radiator fan relay and the ECM or for a faulty ECM.
3. Checks for an open IG fuse or an open in the BLK/WHT wire between the radiator fan relay and the junction block
4. Checks for an open RDTR fuse or an open in the BLK/BLU wire between the radiator fan relay and the fuse box.
5. Check for a faulty radiator fan relay or for a open BLU/RED or BLU wire between the radiator fan relay and the radiator fan motor or for a faulty radiator fan motor.
6. Checks for a short to voltage in the BLU/RED or BLU wire between the radiator fan relay and the radiator fan motor.
7. Checks for a short to ground in the BLU wire between the radiator fan relay and the ECM or for a faulty radiator fan relay or ECM.

DIAGNOSTIC AIDS
If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over, or the warning indicator light, or temperature gage indicated overheating.

If the gage, or light, indicates overheating, but no boil over is detected, the gage or light circuit should be checked. The gage accuracy can also be checked by comparing the coolant sensor reading using a scan tool with the gage reading.

If the engine is actually overheating, and the gage indicates overheating, but the radiator fan is not coining "ON," the ECT sensor has probably shifted out of calibration and should be replaced. Refer to Diagnostic Trouble Code (DTC) 14 chart for the "Temperature vs. Resistance" chart. DTC 14

If the engine is overheating, and the radiator fan is "ON," the cooling system should be checked. Refer to Cooling System. Cooling System