The engine control module (ECM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate a fan, the ECM applies ground to the coil side of the applicable fan relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the relay.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling System Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTCs P0480, P0481, or P0482 are not set.

⇒	If any of the above DTCs are set, refer to DTC P0480, P0481, or P0482.

2. Ignition ON, command the fan relays ON and OFF with a scan tool. The cooling fans should operate with the appropriate commands.

1. Ignition OFF, disconnect the cooling fan relays.
2. Ignition ON, verify that the cooling fans are not operating.

⇒	If a fan is operating, test the appropriate relay controlled output circuit for a short to voltage.

3. If all circuits test normal, test or replace the cooling fan relay.

1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 70-110 Ω between terminals 85 and 86.

⇒	If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified range, replace the relay.

4. Test for less than 2 Ω between the relay terminals 30 and 87A.

⇒	If greater than the specified range, replace the relay.

5. Install a 20 A fused jumper wire between relay terminal 85 and B+. Install a jumper wire between the relay terminal 86 and ground. Test for less than 2 Ω between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement