Windshield Wiper System

The body control module (BCM) controls the wiper motor based on an input from the wiper switch, and when wiper operation is requested, the BCM will send serial data messages to the windshield wiper motor module. The front wiper system consists of a driver's side and passenger's side wiper arm which are connected by a mechanical linkage driven by the windshield wiper motor module. The windshield wiper motor module contains the necessary electronics, motor, and position sensors to execute front wiper commands from the BCM. The windshield wiper motor module clears the front windshield by controlling the up and down wiper arm movement by the use of a reversing motor and an internal position sensor. The sensor keeps track of the gear wheel position and when the windshield wiper motor module determines that the wiper arms are at a position to reverse direction, it reverses the motor supply voltage by use of its internal motor control circuitry. The BCM communicates with the windshield wiper motor module through serial data. The windshield wiper motor module provides system status and diagnostic information to the BCM for diagnostic reporting and operational purposes.

The BCM utilizes resistive multiplexing through the wiper switch to discern the requested action from the driver. The BCM will respond by commanding the specific wiper function to operate as follows:

1. Using intermittent wipes, the wipers pause briefly on the windshield. If the wiper level is moved to OFF or if additional wipes are not required, the wipers may move to the base of the windshield.
2. If the ignition is put in OFF while the wipers are on LO, HI, or INT, they will immediately stop.
3. If the ignition is put in OFF while the wipers are performing wipes due to windshield washing, the wipers continue to run until they reach the base of the windshield.

The windshield wiper system MIST operation is identical to LOW speed operation, except that the MIST switch is a press and release type switch. When the wiper switch is moved to the MIST position (1X) and released, low speed wiper motor operation is started and will continue until 1 cycle is complete. If the wiper switch is moved to the MIST position and held, the wiper motor will operate in the LOW speed mode until the switch is released.

To initiate high speed wiping operation, the BCM provides continuous high speed wiper operation through setting the serial data signal to high speed Wipe. When the wiper switch lever is moved to the high position (HI) and released, high speed wiper motor operation is started and high speed wiping operation is performed.

Fig 1: Front Wiper Block Diagram

Courtesy of GENERAL MOTORS COMPANY