Cooling Fan Functional Check

Circuit Description

Power for the fan motors is supplied through the Underhood Accessory Wiring Junction Block. The cooling fan relays are energized when current flows from the Cool Fan 1 MaxiFuse in the Underhood Accessory Wiring Junction Block and Cool Fan 2 MaxiFuse in the Underhood Accessory Wiring Junction Block through the relay coils to ground through the PCM. The Low Speed Fans Control circuit is grounded for low speed fans operation. The Low Speed Fans Control circuit and the High Speed Fans Control circuits are all grounded for high speed fans operation.

During low speed fans operation the PCM supplies a ground path for the Cool Fan 1 Relay. This closes Cool Fan 1 Relay contacts, allowing current to flow from the Underhood Accessory Wiring Junction Block through the relay contacts to the left hand cooling fan motor. During low speed operation, the ground path for the right hand cooling fan motor is through the Cool Fan 2 Relay and the left hand 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 Cool Fan 1 Relay. The PCM also supplies a ground path for Cool Fan 2 and Cool Fan 3 Relay. This closes all three cooling fan relays. During high speed fans operation, both the right and the left hand engine cooling fans are supplied current from the Underhood Accessory Wiring Junction Block and each cooling fan has its own ground path.

Diagnostic Aids

If the owner complained of an overheating problem, determine if the complaint was due to an actual boil over, or the warning indicator illuminated, or the engine coolant temperature gauge indicated overheating. The gauge accuracy can also be checked by comparing the ECT Sensor reading using a scan tool and comparing its reading with the gauge reading. If the engine is actually overheating and the gauge indicated overheating, but the cooling fan(s) are turning on, the ECT sensor may have shifted out of calibration and should be replaced. If the engine is overheating and the cooling fans are on, the cooling system is suspect and should be checked.

Check for the following conditions:

Important: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Diagrams.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.

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.