Electric Cooling Fan Diagnosis

CIRCUIT DESCRIPTION:
Power for the fan motors is supplied through 2 MaxiFuse in the U/H Electrical Center. The cooling fan relays are energized when current flows from the 2 Maxifuses� through the relay coils to ground through the PCM. The Coolant Fan #1 Relay (Cool Fan 1 Relay) control circuit is grounded for low speed fans operation. The Coolant Fan #1 Relay control circuit and the Coolant Fan #2 Relay control circuit (Cool Fan Relay and Cool Fan 2 Relay) are grounded for high speed fans operation.

During low speed fans operation the PCM supplies a ground path for Cool Fan 1 Relay. This closes the Cool Fan 1 Relay contacts, allowing current to flow from the U/H Electrical Center through the relay contacts to the left engine cooling fan. During low speed operation, the ground path for the primary cooling fan is through the engine Cool Fan Relay and the right 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 Cool Fan 1 Relay. The PCM also supplies a ground path for Cool Fan Relay and Cool Fan 2 Relay. This closes all three cooling fan relays. During high speed fans operation, both the right and the left engine cooling fans are supplied current from the 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.