Radiator Cooling Fan: Testing and Inspection
Engine Cooling Fan Circuit CheckWiring Diagram:
Circuit Description
The engine cooling fan circuit operates the main cooling fan and the auxiliary cooling fan. The cooling fans are controlled by the Engine Control Module (ECM) based on inputs from the Engine Coolant Temperature (ECT) sensor and the Air Conditioning Pressure (ACP) sensor. The ECM controls the low speed cooling fan operation by internally grounding the ECM connector terminal A26. This energizes the low speed cooling fan relay and operates the main cooling fan and the auxiliary cooling fan at low speed as the cooling fans are connected in a series circuit. The ECM controls the high speed cooling fan operation by internally grounding the ECM connector terminal A26 and the ECM connector terminal A51 at the same time. This energizes the low speed cooling fan relay, the high speed cooling fan relay, and the series/parallel cooling fan relay resulting in high speed fan operation as the cooling fans are now connected in a parallel circuit.
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 engine coolant temperature gauge indicated overheating. If the engine is overheating and the cooling fans are ON, the cooling system should be checked.
- If the engine fuse block fuses Ef4 or Ef7 become open (blown) immediately after installation, inspect for a short to ground in the wiring of the appropriate circuit. If the fuses become open (blown) when the cooling fans are to be turned ON by the Engine Control Module (ECM), suspect a faulty cooling fan motor.
- The ECM will turn the cooling fans ON at low speed when the coolant temperature is 96°C (205°F).
- The ECM will turn the cooling fans ON at high speed when the coolant temperature is 99°C (210°F).
- The ECM will turn the cooling fans ON at low speed when the A/C system is ON. The ECM will change the cooling fans from low speed to high speed when the high side A/C pressure is 1,862 kPa (270 psi) then return to low speed when the high side A/C pressure is 1,449 kPa (210 psi).
- The cooling fan circuit can be checked quickly by disconnecting the ECM white connector and grounding the connector terminal A26. This should create low speed cooling fan operation with the ignition ON. By grounding the ECM connector terminals A26 and A51 and turning the ignition ON, high speed cooling fan operation should be achieved.
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Troubleshooting