Wiper Motor: Description and Operation

The rear wiper motor (2) is concealed within the lift-gate, below the liftgate glass and behind the liftgate inner trim panel. The end of the motor output shaft (1) that extends through the liftgate outer panel to drive the rear wiper arm and blade is the only visible component of the rear wiper motor. A rubber bezel and grommet is engaged within the output shaft hole of the liftgate outer panel and seals the output shaft where it passes through the panel. An integral connector receptacle (4) connects the rear wiper motor to the vehicle electrical system through a dedicated take out and connector of the liftgate wire harness. The rear wiper motor consists of the following major components:
- Bracket (5) - The rear wiper motor bracket consists of a molded plastic mounting plate for the wiper motor that is secured with screws to the wiper motor housing, and through three rubber isolators (3) to the liftgate inner panel.
- Motor - The single-speed permanent magnet rear wiper motor is secured with screws to me rear wiper motor bracket. the wiper motor includes an integral transmission, a motor output shaft, an automatic resetting circuit breaker, and the rear wiper motor park switch.

The rear wiper motor cannot be adjusted or repaired. If any component of the motor is faulty or damaged, the entire rear wiper motor unit must be replaced. The motor output shaft bezel and grommet, nut, and nut cover are available for individual service replacement.

The rear wiper motor operation is controlled by the rear wiper relay, which controls battery current flow to the rear wiper motor brushes based upon control outputs from the Front Control Module (FCM). The FCM uses internal programming, hard wired outputs from the rear wiper motor park switch, and electronic messages received over the Controller Area Network (CAN) data bus from the ElectroMechanical Instrument Cluster (EMIC) and from rear wiper and washer switches in the heater-A/C control to determine when to energize or de-energize the rear wiper relay.

The rear wiper motor park switch is a single pole, single throw, momentary switch within the wiper motor that is mechanically actuated by the wiper motor transmission components. The park switch alternately closes and opens a path to ground for the rear wiper motor control circuit input to the FCM, depending upon the position of the rear wiper blade on the liftgate glass. This feature allows the FCM to monitor the number of rear wiper motor cycles, as well as to keep the rear wiper relay energized long enough for the motor to complete its current wipe cycle after the wiper system or the ignition has been turned Off, and to park the wiper blade in the lowest portion of the wipe pattern.

The rear wiper motor is grounded at all times through a take out with an eyelet terminal connector in the body wire harness that is secured to a ground location in the passenger compartment. The automatic resetting circuit breaker protects the motor from overloads. The rear wiper motor transmission converts the rotary output of the wiper motor to the back and forth wiping motion of the rear wiper arm and blade on the liftgate glass.

The hard wired inputs and outputs of the rear wiper motor may be diagnosed using conventional diagnostic tools and methods. However, conventional diagnostic methods may not prove conclusive in the diagnosis of the EMIC, the FCM, the heater-A/C control, CAN data bus, or the electronic message inputs used to control rear wiper motor operation. The most reliable, efficient, and accurate means to diagnose the EMIC, the FCM, the heater-A/C control, the CAN data bus, and the electronic message inputs and outputs that control rear wiper motor operation requires the use of a diagnostic scan tool.