Wiper On/Off Relay: Operation

WARNING: This page is about a different car, the 2005 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.

The wiper on/off relay is an electromechanical switch that uses a low current input from the Body Control Module (BCM) to control a high current output to the front wiper motor. 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 wiper on/off relay terminals are connected to the vehicle electrical system through a connector receptacle in the Power Distribution Center (PDC). The inputs and outputs of the wiper on/off relay include:

Common Feed Terminal - The common feed terminal (30) is connected to the common feed terminal of the wiper high/low relay at all times through the wiper on/off relay output circuit. Therefore, the wiper high/low relay is able to control the wiper motor speed only when the wiper on/off relay is energized.
Coil Ground Terminal - The coil ground terminal (85) is connected to a control output of the Body Control Module (BCM) through the front wiper on/off relay control circuit. The BCM controls front wiper motor operation by controlling a ground path through this circuit.
Coil Battery Terminal - The coil battery terminal (86) receives battery current at all times from a circuit breaker in the Junction Block (JB) through a fused ignition switch output (run-acc) circuit.
Normally Open Terminal - The normally open terminal (87) receives battery current from a circuit breaker in the Junction Block (JB) through a fused ignition switch output (run-acc) circuit. When the front wiper on/off relay is energized, the wiper high/low relay is able to control the wiper motor speed.
Normally Closed Terminal - The normally closed terminal (87A) is connected to the wiper park switch in the front wiper motor through the front wiper park switch sense circuit, and is connected to the wiper park switch whenever the relay is de-energized.

The wiper on/off relay can be diagnosed using conventional diagnostic tools and methods.