Cooling Fan Functional Check

Refer to Engine Controls Schematic Cooling Fans.

Diagnostic Chart:

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 Powertrain Control Module (PCM) supplies a ground path for the Cooling 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, Cooling 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 Cooling Fan 1 relay through the Low Speed Fans control circuit. After a 3 second delay, the PCM supplies a ground path for the Cooling Fan 2, series/parallel, and Cooling 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:
^ When A/C is requested and ambient temperature is more than 50°C (122°F).
^ When engine coolant temperature exceeds 106°C (223°F).
^ When A/C refrigerant pressure is more than 190 psi (2 volts).
^ When the ignition is OFF and engine coolant temperature is more than 140°C (284°F).

The PCM will command high speed cooling fans operation under any of the following conditions:
^ When engine coolant temperature exceeds 110°C (230°F).
^ When A/C refrigerant pressure is more than 240 psi (2.5 volts).

DIAGNOSTIC AIDS
Inspect 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
- 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 DTCs 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.