Electric Cooling Fan Diagnosis

Circuit Description

The engine cooling fans receive power from two separate 30 amp Maxifuses located in the Underhood Electrical Center.

During low speed operation, the PCM supplies a ground path for the Cool Fan 1 relay through the Low Speed Fans Control circuit. This energizes the relay coil, closes the Fan 1 relay contacts, and supplies current to engine cooling fan # 1 motor. The ground path for engine cooling fan # 1 motor is through the series/parallel cooling fan relay (Cool Fan 2 relay) and engine cooling fan # 2 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 engine cooling fan motors are supplied current through their respective Maxifuse and each fan has its own ground path.

The PCM will command Low Speed Cooling Fans operation under any of the following conditions:

VIN K
^ When A/C is requested and ambient temperature is greater than 50°C (122°F).
^ When engine coolant temperature exceeds 106°C (223°F).
^ When A/C refrigerant pressure is greater than 190 psi (2 volts).
^ When the ignition is off and engine coolant temperature is greater than 140°C (284°F).

VIN 1
^ When A/C is requested and ambient temperature is greater than 40°C (104°F).
^ When engine coolant temperature exceeds 100°C (212°F).
^ When A/C refrigerant pressure is greater than 190 psi (2 volts).
^ When the ignition is off and engine coolant temperature is greater than 140°C (284°F).

The PCM will command High Speed Cooling Fans operation under any of the following conditions:

VIN K
^ When engine coolant temperature exceeds 110°C (230°F).
^ When A/C refrigerant pressure is greater than 240 psi (2.5 volts).

VIN 1
^ When engine coolant temperature exceeds 108°C (226°F).
^ When A/C refrigerant pressure is greater than 240 psi (2.5 volts).

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.