Cooling Fan Functional Check

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 Maxifuses are 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 fans. 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.

Important: When certain Diagnostic Trouble Codes (DTCs) are present, the PCM may command the cooling fans to run all the time. It is important to perform the Powertrain On-Board Diagnostic System check prior to diagnosing the engine cooling fans. The PCM commands low speed fans operation under the following conditions: Initial Inspection and Diagnostic Overview

VIN K

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

VIN 1

^ When engine coolant temperature exceeds 100°C (223°F).
^ When A/C is requested and ambient temperature is greater than 40°C (104°F)
^ When A/C refrigerant pressure is greater than 190 psi (2 volts).
^ When the ignition switch is turned off and engine coolant temperature is greater than 140°C (284°F).

The PCM commands high speed fans operation under 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

The numbers below refer to numbers on the diagnostic table.

2. The PCM will enable the engine cooling fans when certain Diagnostic Trouble Codes are set. Go to applicable DTC Table first before proceeding with this table.
3. Allow engine coolant temperature to cool below 100°C (212°F) before proceeding with diagnosis.