Relay-Wiper On/Off: Operation

WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. 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 front control module (FCM) to control a high current output to the 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 integrated power module (IPM). 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.
Coil Ground Terminal - The coil ground terminal (85) is connected to a control output of the FCM through a wiper on/off relay control circuit. The FCM controls 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 fuse in the power distribution center (PDC) through a fused ignition switch output (run-acc) circuit.
Normally Open Terminal - The normally open terminal (87) receives battery current at all times from a fuse in the PDC through a fused ignition switch output (run-acc) circuit, and provides battery current to the wiper on/off relay output circuit whenever the relay is energized.
Normally Closed Terminal - The normally closed terminal (87A) is connected to ground at all times through a take out of the headlamp and dash wire harness with an eyelet terminal connector that is secured by a screw to the front end sheet metal, and is connected to the wiper on/off relay output circuit whenever the relay is de-energized.

The wiper on/off relay may be diagnosed using conventional diagnostic tools and methods. However, conventional diagnostic methods may not prove conclusive in the diagnosis of the steering control module (SCM), FCM or the electronic message inputs to or outputs from the SCM and the FCM that control the operation of the wiper on/off relay. The most reliable, efficient, and accurate means to diagnose the wiper on/off relay, SCM, FCM or the electronic message inputs and outputs related to the wiper on/off relay operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.