Electric Cooling Fan Diagnosis

Circuit Description
The Electric Cooling Fan(s) are controlled by the Body Control Module (BCM) which enables the fans through the PCM. The PCM enables the ground path for the three cooling fan relays. The relay(s) are used to control the high current flow to power the cooling fan motors. When minimum cooling is required, the BCM will command the PCM to energize cooling fan relay #1 and since both fans are connected in series through the Mode Control relay, both fans will operate at low speed. When maximum cooling is required, the BCM will communicate to the PCM to energize all three cooling fan relays. Power is supplied to the left fan through the Mode Control relay. The right fan is powered directly through cooling fan relay #2 causing both fans to operate at high speed.

Diagnostic Aids
If the owner complained of an overheating problem, determine if the complaint was due to an actual boil over, or the warning indicator illuminated, or the Engine Coolant Temperature gauge indicated overheating. The gauge accuracy can also be checked by comparing the ECT Sensor reading using a scan tool and comparing its reading with the gauge reading. If the engine is actually overheating and the gauge indicated overheating, but the cooling fan(s) are turning on, the ECT sensor may have shifted out of calibration and should be replaced. If the engine is overheating and the cooling fans are on, the cooling system is suspect and should be checked. Refer to Engine Overheating in Engine.
Check for the following conditions:
^ Poor connection at the PCM, cooling fan relays, or cooling fan motors. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Intermittents and Poor Connections Diagnosis.
^ Damaged harness. Inspect the wiring harness for damage. Refer to Intermittents and Poor Connections. Symptom Related Diagnostic Procedures

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
2. Stored diagnostic trouble codes may affect engine cooling fans operation. This diagnostic table may lead to improper diagnosis and replacement of good parts if diagnostic trouble codes are present.
6. Ambient temperature must be above 9°C (48°F) before the PCM will enable the cooling fans due to A/C request. The PCM will enable the cooling fans if A/C refrigerant pressure increases regardless of ambient temperature.
77. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.