Commander 4WD V8-4.7L VIN N (2006)
The FCM controls the hard wired outputs to the pump motor based upon electronic washer request messages received over the Controller Area Network
(CAN) data bus from the Steering Control Module (SCM). The SCM monitors a resistor multiplexed input from the front and rear washer switch
circuitry contained within the right (wiper) multi-function switch to determine the proper washer request message to send. Whenever the low washer
fluid indicator is illuminated, the FCM is programmed to suppress all rear washer requests in order to give priority to the vehicle operator s need for
forward visibility.
Washer fluid is gravity-fed from the washer reservoir to the inlet port of the washer pump housing. An integral valve body is located in a housing on the
outlet port side (2) of the pump housing. A diaphragm (4) in this valve body controls which washer system plumbing receives the washer fluid being
pressurized by the pump. When the pump is not operating the diaphragm is biased to close all washer fluid flow in the rear washer system and, in this
way it also performs the function of the rear washer system check valve.
When the pump impeller (1) rotates in the counterclockwise direction (viewed from the bottom), the biased diaphragm is sealing off the rear washer
system outlet and nipple so the pressurized washer fluid is pushed out through the pump front outlet port and the front washer outlet nipple (5). When the
pump impeller rotates in the clockwise direction (viewed from the bottom), pressurized washer fluid is pushed out through the pump rear outlet port and
moves the diaphragm to open the rear washer outlet nipple and seal off the front washer outlet nipple, then the pressurized washer fluid is pushed out
through the rear washer outlet nipple (3).
The washer pump/motor unit and the hard wired motor control circuits from the FCM may be diagnosed and tested using conventional diagnostic tools
and procedures. However, conventional diagnostic methods may not prove conclusive in the diagnosis of the FCM, the SCM, the CAN data bus or the
electronic messages used to provide washer pump/motor unit control. The most reliable, efficient, and accurate means to diagnose the FCM, the SCM,
the CAN data bus and the electronic messages for the washer pump/motor unit control requires the use of a diagnostic scan tool.
