Functional Check - Electric Cooling Fan

CIRCUIT DESCRIPTION:

Power for the fan motors is supplied through the U/H Electrical Center. The cooling tan relays are energized when current flows from the Cool Fan #1 Fuse in the U/H Electrical Center (U/H BEC) and Cool Fan #2 fuse in the U/H Electrical Center (U/H BEC) through the relay coils to ground through the PCM. The #1 Fan control Relay circuit is grounded for low speed fans operation. The #1 Fan Control Relay control circuit and the Mode control relay (cool fan series) and #2 Fan Control Relay circuits are all grounded for high speed fans operation.

During low speed fans operation the PCM supplies a ground path for the #1 Fan Control Relay. This closes the #1 Fan Control relay contacts, allowing current to flow from the U/H Electrical Center through the relay contacts to the left hand cooling fan motor. During low speed operation, the ground path for the left hand cooling fan motor is through the #2 Fan Control Relay and the right hand engine cooling fan motor. The result is a series circuit with both cooling fans running at low speed.

During high speed cooling fan operation the PCM supplies a ground path for the #1 Fan control Relay. The PCM also supplies a ground path for #2 Fan Control Relay and the Mode control relay (cool fan series). This closes all three cooling fan relays. During high speed fans operation, both the right and the left hand engine cooling fans are supplied current from the Underhood Bussed Electrical Center (U/H ELECTRICAL CENTER) and each cooling fan has its own ground path.


DIAGNOSTIC AIDS

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.

^ Damaged harness. Inspect the wiring harness for damage.


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. Refer to PCM Replacement/Programming.