Electric Cooling Fan Diagnosis

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

Power for the fan motors is supplied through the Cooling Fan fuse in the RH Maxi fuse block. The cooling fan relays are energized when current flows from the Cooling Fan fuse in the P fuse block through the relay coils to ground through the PCM. The cooling fan 1 control circuit is grounded for low speed fan operation. The cooling fan 1 and cooling fan 2 control circuits are grounded for high speed operation.

During low speed fan operation the PCM supplies a ground path for the low speed cooling fan relay #1. This closes the low speed relay contacts, allowing current to flow from the battery junction block through the relay contacts to the primary cooling fan. During low speed operation, the ground path for the primary cooling fan is through the series/parallel cooling fan relay and secondary cooling fan motor. The result is a series circuit with both fans running at low speed.

During high speed cooling fan operation the PCM supplies a ground path for the low speed cooling fan relay through the cooling fan 1 control circuit. The PCM also supplies a ground path for the high speed cooling fan relay #3 and the series/parallel cooling fan relay #2 through the cooling fan 2 control circuit. This closes all three fan relays. During high speed operation, both the primary and the secondary cooling fans are supplied current from the battery junction block and each 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 greater than 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.