Circuit/System Description

The body control module (BCM) controls the rear wiper motor based on an input from the rear wiper switch, which is part of the windshield wiper/washer switch. The BCM monitors the windshield wiper/washer switch through two separate signal circuits and a low reference circuit. The rear wiper switch uses a resistor ladder to determine low speed, intermittent, and rear washer operation. The BCM monitors applies and monitors voltage on the rear wiper switch signal circuit. When the rear wiper switch is placed in the low speed, intermittent, or rear washer position, the voltage is pulled down through a different resistor in the resistor ladder, reducing the voltage seen at the BCM. The BCM will respond by commanding the specific rear wiper function.

The rear wiper motor is controlled by the BCM through the rear wiper relay. A constant B+ and ground are supplied to the rear wiper motor. When rear wiper operation is requested, the BCM will apply voltage to the rear wiper relay control circuit. This will cause the contacts in the rear wiper relay to close and apply B+ to the rear wiper motor through the rear wiper control circuit, enabling rear wiper operation. When the rear wiper request is no longer present, the contacts in the rear wiper relay will open, removing B+ from the rear wiper motor control circuit. The rear wiper motor will continue to operate using the constant B+ circuit until it is in the park position.