Cooling Fan Functional Check

Diagnostic Chart:

CIRCUIT DESCRIPTION
Power for the fan motors is supplied through the underhood junction block. Refer to Engine Control Components Underhood Junction Block. The cooling fan relays are energized when current flows from the Cool Fan #1 fuse and the Cool Fan #2 fuse in the underhood junction block through the relay coils to ground through the Powertrain Control Module (PCM). The LH fan control circuit is grounded for low speed fans operation. The LH fan control circuit and the RH fan control circuits are both grounded for high speed fans operation.

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

During high speed fans operation the PCM supplies a ground path for the #1 fan control relay and then the mode control and the #2 fan control relay. This closes all 3 cooling fan relays. During high speed fans operation, both the LH cooling fan motor and the RH cooling fan motor are supplied current from the underhood junction block and each cooling fan has its own ground path through the ground splice pack. Refer to Engine Control Components Ground Splice Pack.

DIAGNOSTIC AIDS
If the owner complained of an overheating problem, determine if the complaint was due to an actual boil over, the warning indicator illuminated, or the engine coolant temperature gauge indicated overheating. The gauge accuracy can also be tested 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 fans are not 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 inspected.

Inspect 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 inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Diagrams.
^ PCM and engine grounds for clean and secure connections

If the DTC is determined to be intermittent, reviewing the Failure 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 DTCs are set. Refer to applicable DTC table first before proceeding with this table.
3. Allow ECT to cool below 1OO°C (212°F) before proceeding with diagnosis.