Relay-Wiper High/Low: 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 high/low 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 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 high/low 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 high/low relay include:

Common Feed Terminal - The common feed terminal (30) is connected to the output of the wiper on/off 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 high/low 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) is connected to the high speed brush of the wiper motor through a wiper high/low relay high speed output circuit, and is connected to the high speed brush whenever the relay is energized.
Normally Closed Terminal - The normally closed terminal (87A) is connected to the low speed brush of the wiper motor through a wiper high/low relay low speed output circuit, and is connected to the low speed brush whenever the relay is de-energized.

The wiper high/low relay can 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 high/low relay. The most reliable, efficient, and accurate means to diagnose the wiper high/low relay, SCM, FCM or the electronic message inputs and outputs related to the wiper high/low relay operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.