Wiper Relay: Operation

WARNING: This page is about a different car, the 2003 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

The wiper relay (or intermittent wipe relay) is an electromechanical switch that uses a low current input from the Central Timer Module (CTM) to control a high current output to the low speed brush of 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 or diode 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 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 relay include:

Common Feed Terminal -The common feed terminal (30) is connected to the wiper motor low speed brush through the wiper control circuitry of the multi-function switch on the steering column. When the wiper relay is de-energized, the common feed terminal is connected to the wiper park switch output through the CTM on the front wiper park switch sense circuit. The wiper park switch output may be battery current (wipers are not parked), or ground (wipers are parked). When the wiper relay is energized, the common feed terminal of the relay is connected to battery current from a fuse in the Junction Block (JB) through a fused ignition switch output (run-acc) circuit.
Coil Ground Terminal -The coil ground terminal (85) is connected to the relay control output of the CTM through the wiper relay control circuit. The CTM controls the ground path for this circuit internally to energize or de-energize the wiper relay based upon its programming, inputs from the wiper and washer control circuitry of the multi-function switch, and inputs from the wiper motor park switch.
Coil Battery Terminal -The coil battery terminal (86) is connected to battery current from a fuse in the Junction Block (JB) through a fused ignition switch output (run-acc) circuit whenever the ignition switch is in the On or Accessory positions.
Normally Open Terminal -The normally open terminal (87) is connected to battery current from a fuse in the Junction Block (JB) through a fused ignition switch output (run-acc) circuit whenever the wiper relay control coil is energized by the CTM. This circuit provides fused ignition switch output (run-acc) current to the wiper motor low speed brush only when the wiper relay control coil is energized.
Normally Closed Terminal -The normally closed terminal (87A) is connected to the output of the wiper motor park switch through the CTM on the front wiper park switch sense circuit. This circuit provides battery current (wipers are not parked) or ground (wipers are parked) to the wiper motor low speed brush whenever the wiper relay control coil is de-energized and the Off position of the wiper control circuitry within the multi-function switch is selected.

The wiper relay may be diagnosed using conventional diagnostic tools and methods. However, conventional diagnostic methods may not prove conclusive in the diagnosis of the CTM, or the inputs to or outputs from the CTM that control the operation of the wiper relay. The most reliable, efficient, and accurate means to diagnose the wiper relay and the CTM inputs and outputs related to the wiper relay operation requires the use of a DRBIII(R) scan tool. Refer to the appropriate diagnostic information.