Rear Wiper System: Notes

On vehicles equipped with a Rear Wiper, the rear wiper system consists of the rear wiper relay and the rear wiper motor. The BCM determines of the Rear Wipe/Wash System Mode of Operation (Intermittent, ON, OFF) by monitoring the output of the Rear Wipe/Wash Switch. The rear wiper switch provides a request to the BCM. The BCM activates the output and applies Battery to the coil of the relay, the relay energizes, allowing Battery voltage from the fuse to be applied through the switched contacts of the Rear Wiper Motor Relay to the Rear Wiper Motor. The rear wiper motor then operates continuously at low speed, uses a reference ground signal from the BCM for the Rear Wiper/Washer Switch output signal it receives. The Rear Wiper/Washer signal received by the BCM is the result of 3 resistors in the Rear Wiper Switch configured as a resistor ladder network. This signal is connected to a BCM Analog to Digital Input which also provides a switched Battery pull-up for the circuit. Depending on the function selected (Intermittent, ON, OFF, Wash), the Rear Wiper Control Switch connects a different set of resistors into the circuit resulting in different voltages appearing on the BCM A/D input. By monitoring this voltage, the BCM determines how to control the Rear Wiper Motor Relay and the Rear Washer Relay.

The BCM does not control the parking of the Rear Wiper Motor, it is self parking. When the BCM deactivates its output, the contacts of the Rear Wiper Motor Relay switch back to ground. The Rear Wiper's internal park switch and circuitry will sustain motor operation until the wiper arm has returned to its Park position.