Grand Cherokee 2WD V6-3.7L (2008)
Headlamp Washer Motor Relay: Description and Operation
Operation
OPERATION
The headlamp washer relay is an electromechanical switch that uses a low current input from the Front Control Module (FCM) to control a high current
output to the headlamp washer pump/motor unit. The movable common feed contact point is held against the fixed normally closed contact point by
spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the
movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the
relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. A resistor is connected
in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the
electromagnetic field of the relay coil collapses.
The headlamp washer relay terminals are connected to the vehicle electrical system through a connector receptacle in the Integrated Power Module
(IPM). The inputs and outputs of the headlamp washer relay include:
-
Common Feed Terminal - The common feed terminal is connected to battery current from a fuse in the IPM through a fused B(+) circuit at all
times.
-
Coil Ground Terminal - The coil ground terminal is connected to ground at all times through a take out with an eyelet terminal located on the
sheet metal within the engine compartment.
-
Coil Battery Terminal - The coil battery terminal is connected to a high side driver output from the FCM. The FCM controls headlamp washer
system operation through this relay connection.
-
Normally Open Terminal - The normally open terminal is connected to the headlamp washer pump/motor unit at all times. When the relay is
energized, the normally open terminal of the relay is connected to battery current from the fuse in the IPM.
-
Normally Closed Terminal - The normally closed terminal is not connected to any circuit in this application, but provides a battery current
output only when the headlamp washer relay coil is de-energized.
The headlamp washer relay as well as the hard wired inputs and outputs of the relay may be diagnosed using conventional diagnostic tools and
procedures. Refer to the appropriate wiring information.
