Rear Wiper Relay - Operation

OPERATION

The rear wiper 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 rear wiper module. 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 rear wiper relay terminals are connected to the vehicle electrical system through soldered connections to the electronic circuit board of the Junction Block (JB). The inputs and outputs of the rear wiper relay include:

- Common Feed Terminal - The common feed terminal (30) is connected to battery current from a fuse in the PDC through a fused B(+) circuit at all times.
- Coil Ground Terminal - The coil ground terminal (85) is connected to a control output of the FCM through a rear wiper relay control circuit. The FCM energizes and de-energizes the rear wiper module by controlling a ground path through this circuit.
- Coil Battery Terminal - The coil battery terminal (86) is connected to battery current from a fuse in the PDC through a fused B(+) circuit at all times.
- Normally Open Terminal - The normally open terminal (87) is connected to the rear wiper module through the rear wiper relay output circuit. When the rear wiper relay is energized, the normally open terminal of the relay is connected to battery current from a fuse in the Power Distribution Center (PDC) through a fused B(+) circuit.
- Normally Closed Terminal - The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the rear wiper relay coil is de-energized.

The rear wiper 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.