Circuit Operation

The Powertrain Control Module (PCM) controls both cooling fans by controlling three relays through two outputs. There are two modes of cooling fan operation: low speed and high speed. In the low speed mode, the cooling fans are powered in series. The PCM energizes Cooling Fan Relay #1, causing both cooling fans to run at low speed. in the high speed mode the cooling fans are powered in parallel which runs the fans at high speed. The PCM energizes all three cooling fan relays during high-speed mode.

Low Speed Operation
Low speed cooling fan operation occurs when the PCM grounds the Cooling Fan Relay #1 coil on DK GRN (335). With only Cooling Fan Relay #1 energized, voltage is applied to both the LH and RH Cooling Fan Motors. Power is supplied to the motors through the Cooling Fan Relay #1 contacts, circuits BLK (532), WHT (504) and LT BLU (409), and the Cooling Fan Relay #2 contacts. The two motors are connected through a series circuit This circuit divides the voltage applied by COOLING FANS Maxi Fuse between the two motors. The division of the voltage causes the motors to operate at a lower speed. In the series mode, the fans are grounded through BLK (1350) and ground G103.

High Speed Operation
The cooling fans run at high speed when the PCM grounds Cooling Fan Relays #1, #2, and #3 on circuits DK GRN (335) and DK BLU (473). With both Cooling Fan Relay #1 and Cooling Fan Relay #3 energized, battery voltage is applied to the LH Cooling Fan Motor through the relay contacts. The LH Cooling Fan Motor runs at high speed because the fan motor is grounded directly through the contacts of Cooling Fan Relay #1, Cooling Fan Relay #3, BLK (1350) and ground G103.

Since Cooling Fan Relay #2 is also energized during high speed operation, battery voltage is applied directly to the RH Cooling Fan Motor through the closed contacts of the relay. The fan runs at high speed since it is no longer in series with the LH Cooling Fan Motor.