The engine control module (ECM) commands the auxiliary or pusher cooling fan On when the engine coolant temperature exceeds a calibrated value. In normal operation, the left and right cooling fans will activate first at low speed, second at high speed, and third the pusher fan will activate if the coolant temperature continues to increase. The ECM applies ground to the coil side of the pusher fan relay. This energizes the coil and applies voltage directly to the fan through the switch side of the relay.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

1. Ignition OFF, disconnect the PUSHER FAN relay.
2. Ignition ON, observe that fan is not activated.

⇒	If the fan is still activated, test for a short to voltage in the relay controlled output circuit terminal R8.

⇒	If the fan is not activated, test or replace the relay.

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

⇒	If the resistance is 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. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Auxiliary Engine Coolant Fan and Fan Motor Replacement