Without A/C

Engine Cooling Fan Circuit Check - Without A/C

Circuit Description
The engine cooling fan circuit operates the cooling fan. The cooling fan is controlled by the powertrain control module (PCM)/engine control module (ECM) based on input from the engine coolant temperature (ECT) sensor. The PCM/ECM controls the low speed cooling fan operation by internally grounding the PCM/ECM connector terminal C13. This energizes the low speed cooling fan relay and operates the cooling fan at low speed. The low speed cooling fan operation is achieved by the cooling fan resistor causing a drop in the voltage supplied to the cooling fan. The PCM/ECM controls the high speed cooling fan operation by internally grounding the PCM/ECM connector terminal C12. This energizes the high speed cooling fan relay, bypassing the radiator fan resistor This results in high speed cooling fan operation.

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 I/P fuse block fuse F19 or the engine fuse block fuse EF4 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 fan is to be turned on by the PCM/ECM, suspect a faulty cooling fan motor.
- The PCM/ECM will turn the cooling fans on at low speed when the coolant temperature is 93 °C (199 °F). The PCM/ECM will turn the cooling fans off when the coolant temperature is 90 °C (194 °F).
- The PCM/ECM will turn the cooling fans on at high speed when the coolant temperature is 97 °C (207° F). The PCM/ECM will change the cooling fans from high speed to low speed when the coolant temperature is 94 °C (201 °F)
- The cooling fan circuit can be checked quickly by disconnecting the PCM/ECM 24-pin connector and grounding the connector terminal C13. This should create low speed cooling fan operation with the ignition ON. By grounding the PCM/ECM connector terminals C13 and C12 and turning the ignition ON, high speed cooling fan operation should be achieved.

Steps 1 - 7:

Steps 8 - 20:

Steps 21 - 31:

Test Description
The number(s) below refer to step(s) on the diagnostic table.
4. This step, along with step 5, checks for the ability of the PCM/ECM to operate the cooling fans.
22. By directly grounding the PCM/ECM connector terminals C13 and C12, the cooling fan should run at high speed.