Electric Cooling Fans Inoperative-High Speed Commanded

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Fan Relay Operation Matrix:

Engine Controls Schematics: Cooling Fans and Relays:

CIRCUIT DESCRIPTION
The engine cooling fan system consists of two electric cooling fans and three fan relays that are controlled by the PCM. The cooling fans receive power from a 50A Maxifuses located in the Underhood Fuse Block Assembly. The relays are wired in a series/parallel arrangement that allows the PCM to operate both fans together at low and/or high speed.

During low speed operation, the PCM supplies a ground path for the low speed fans relay through the low speed fans control circuit. This energizes the relay coil, closes the relay contacts, and supplies current to the engine cooling fans. The ground path for the right engine cooling fan is through the series/parallel cooling fan relay and the left engine cooling fan. The result is a series circuit with both fans running at low speed.

To command high speed cooling fan operation the PCM first supplies the ground path for the low speed cooling fans relay through the low speed fans control circuit. After a few seconds delay, the PCM supplies the ground path for the high speed cooling fan relay and the series/parallel cooling fan relay through the high speed fans control circuit. During high speed operation, both engine cooling fans are supplying current through their respective maxifuse and each fan has its own ground path.

To determine if a non-DTC fault is present, perform the Cooling Fan Functional Check. If DTC P0480 or P0481 is set, or either DTC sets during the functional check, the DTCs must be diagnosed before proceeding with any of the symptom tables.

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 (OBD) System Check prior to diagnosing the engine cooling fans.

The PCM commands low speed fans operation under the following conditions:
If the cooling fans operate when commanded off and no DTCs are set, either a cooling fan relay is stuck on or a cooling fan circuit is shorted to power.

Whenever a repair is completed repeat the Cooling Fan Functional Check. The functional check will confirm proper system operation as well as help diagnose possible multiple failures, for example: two water contaminated relays.

DIAGNOSTIC AIDS
If the cooling fans operate when commanded off and no DTCs are set, either a cooling fan relay is stuck on or a cooling fan circuit is shorted to power.

Several circuits (or a portion of a circuit) are part of the Underhood Fuse Block Assembly. Typically if a problem is narrowed down to a circuit that is found within the Underhood Fuse Block Assembly, the entire assembly must be replaced.

If the problem is intermittent refer to Intermittent Conditions Intermittent Conditions

TEST DESCRIPTION
The numbers below refer to the step numbers in the diagnostic table.
5. This step tests the cooling fan relay #2 control circuit.
9. This step tests the cooling fan relay #3 control circuit.