Electric Cooling Fan Diagnosis

Diagnostic Chart:

Diagnostic Chart (cont'd):

Electrical Diagram:

CIRCUIT DESCRIPTION:

Power for the fan motors is supplied through a fusible link at the battery junction block. The cooling fan relays are energized when current flows from the A/P fan fuse through the relay coils to ground through the PCM. The cooling fan relay #1 control circuit is grounded for low speed fans operation. The cooling fan relay #1 control circuit and the cooling fan relay #2 and #3 circuits are both grounded for high speed fans operation.

During low speed fans operation the PCM supplies a ground path for the engine cooling fan relay #1. This closes the engine cooling fan relay #1 contacts, allowing current to flow from the battery junction block 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 cooling fan relay #3 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 engine cooling fan relay #1. The PCM also supplies a ground path for engine cooling fan relay #2 and engine cooling fan relay #3. 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 battery junction block 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.

7. 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.