Engine Cooling Fan Circuit Check - With A/C
Radiator Cooling Fan Motor: Testing and Inspection
Engine Cooling Fan Circuit Check - With A/C
Engine Cooling Fan Circuit Check - With A/C
Circuit Description
The engine cooling fan circuit operates the main cooling fan and the auxiliary cooling fan. The cooling fans are controlled by the powertrain control
module (PCM)/engine control module (ECM) based on inputs from the engine coolant temperature (ECT) sensor and the air conditioning pressure
(ACP) 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 main cooling fan and the auxiliary cooling fan at low speed as the cooling fans are connected
in a series circuit. The PCM/ECM controls the high speed cooling fan operation by internally grounding the PCM/ECM connector terminal C13 and the
PCM/ECM connector terminal C12 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 become open (blown) immediately after installation, inspect for a short to ground in the WI ring of the
appropriate circuit. If the fuses become open (blown) when the cooling fans are 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 97 °C (207 °F). The PCM/ECM will turn the cooling
fans off when the coolant temperature is 94 °C (201 °F).
-
The PCM/ECM will turn the cooling fans on at high speed when the coolant temperature is 101 °C (214 °F). The PCM/ECM will change the
cooling fans from high speed to low speed when the coolant temperature is 98 °C (208 °F).
-
The PCM/ECM will turn the cooling fans on at low speed when the A/C system is on. The PCM/ECM will change the cooling fans from low speed
to high speed when the high side A/C pressure is 1882 kPa (273 psi) then return to low speed when the high side A/C pressure is 1448 kPa (210
psi). When the A/C system is on, the PCM/ECM will change the cooling fans from low to high speed when the coolant temperature reaches 117 °
C (244 °F) then return to low speed when the coolant temperature reaches 114 °C (237 °F).
-
The cooling fan circuit can be checked quickly by disconnecting the PCM/ECM connector 2 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.
