Electric Cooling Fan Diagnosis

Circuit Description:
The engine coolant fan motor #1 receives power from a 40 amp MaxiFuse. The engine coolant fan motor #2 receives power from a 30 amp MaxiFuse. Both of the MaxiFuses are located in the underhood electrical center.

During low speed operation, the powertrain control module (PCM) supplies a ground path for the cool fan 1 relay through the coolant fan #1 relay control circuit. This energizes the relay coil, closes the fan 1 relay contacts, and supplies current to the primary cooling fan. The ground path for the primary cooling fan is through the series/parallel cooling fan relay (cool fan 2 relay) and the secondary cooling fan motor. The result is a series circuit with both fans running at low speed.

To command high speed cooling fan operation the PCM first supplies a ground path for the cool fan 1 relay through the low speed fans control circuit. After a 3 second delay, the PCM supplies a ground path for the cool fan 2 (series/parallel) and cool fan 3 relays through the high speed fans control circuit. During high speed operation, both the primary and the secondary cooling fans are supplied current through their respective Maxifuses and each fan has a ground path.

Diagnostic Aids
Inspect for the following conditions:
^ A faulty connection at the PCM, cooling fan relays, or cooling tan motors. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections.
^ 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.