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<\/a><\/p>\nFig. 7<\/strong><\/p>\n <\/p>\n Wiper and Washer Systems is the eighth topic in the TechLink series highlighting several of the related systems handled by the Body Control Module (BCM) on GM models built with the Vehicle Intelligence Platform (VIP). The goal of this series is to help improve understanding of the components operated by the BCM and reduce warranty claims and unnecessary component replacement.<\/p>\n The earlier systems in the series are the Keyless Entry System<\/strong><\/a>, Content Theft Deterrent<\/a>,<\/strong> Door Latch Actuators<\/a>,<\/strong> Tire Pressure Monitoring Systems<\/strong><\/a>, Exterior and Interior Lighting<\/strong><\/a>, Fixed and Moveable Windows<\/strong><\/a>, and Mirrors<\/a>.<\/strong><\/p>\n COMPONENT BREAKDOWN<\/strong><\/p>\n SWITCH OPERATION<\/strong><\/p>\n The windshield wiper\/washer switch (Fig. 8) contains a resistor ladder network connected to the BCM wiper switch low-signal circuit. The BCM provides the low-signal and low-reference circuits to the switch. It applies approximately 5 V to the low-signal circuit and monitors the resulting voltage drop. The effective resistance of the switch circuit varies with switch position, allowing the BCM to identify mist, off, intermittent, low-speed, and high-speed requests. Based on the detected switch position, the BCM determines the requested wiper operation and sends a serial-data request to the Lighting Control Module.<\/p>\n Fig. 8<\/strong><\/p>\n <\/p>\n High-speed wiper operation requires two inputs. When the wiper switch is placed in the high-speed wipe position, the low-signal resistor ladder switch moves to its high-speed contact, which the BCM interprets the same as a low-speed wipe request. In this position, there is another set of contacts within the switch, which are separate from the resistor ladder network, that will close. These contacts are connected to and monitored by the Lighting Control Module through the wiper switch high-signal circuit. When the contacts are closed, the signal circuit will be connected to ground, pulling the signal voltage from the Lighting Control Module low. When the Lighting Control Module receives a serial data request from the BCM indicating a low\/high-speed wipe request and the wiper switch high-signal circuit is pulled low, the Lighting Control Module will command high-speed wiper operation.<\/p>\n For smart wiper motor systems, the high-speed signal circuit also is monitored directly by the wiper motor, and the wiper motor will command high-speed wiper operation when it receives the serial data message from the BCM and the signal circuit is pulled low. If the Lighting Control Module or smart wiper motor detects that the wiper switch high-speed signal is pulled low, but no serial data message is received from the BCM, the wiper low-speed operation will be commanded.<\/p>\n On vehicles equipped with a rear wiper (Fig. 9), there also may be a second signal circuit provided by the BCM and a second resistor-ladder network within the switch to control rear wipe\/wash operation. The rear wiper motor may be either a basic motor or a smart motor depending on application.<\/p>\n Fig. 9<\/strong><\/p>\n <\/p>\n BASIC WIPER MOTOR OPERATION <\/strong>\u2014 <\/strong>RELAY-OPERATED<\/strong><\/p>\n <\/p>\n Fig. 10<\/strong><\/p>\n <\/p>\n Lighting Control Module<\/strong><\/p>\n The Lighting Control Module controls the windshield wiper motor through two relays. The primary wiper relay enables motor power by applying voltage to its coil, closing the contacts, and supplying fused B+ to the motor circuit. For intermittent operation, the BCM interprets the intermittent setting and, when equipped, rain-sensor information to determine the wipe interval. It then sends the Lighting Control Module requests for low-speed operation at the appropriate times. The Lighting Control Module energizes the primary relay while leaving the speed-control relay de-energized, routing B+ through the normally closed contacts to the motor\u2019s low-speed circuit.<\/p>\n Park Switch<\/strong><\/p>\n The park switch is internal to the windshield wiper motor. As the wipers reach the park position, the park switch closes and pulls the park signal circuit low. The Lighting Control Module monitors this signal to identify the park position. When the wiper request is removed, the Lighting Control Module continues operating the motor until the park signal indicates that the wipers have reached the park position and then removes motor power and applies dynamic braking.<\/p>\n Dynamic Braking<\/strong><\/p>\n Dynamic braking is an electrical stopping method, not a mechanical brake. When the wipers reach the park position, the Lighting Control Module de-energizes the wiper relays. Their normally closed contacts remove B+ and connect the motor control input to ground. The spinning DC motor then acts briefly like a generator, creating current that opposes the motor\u2019s rotation and dissipates the remaining energy as heat. This quickly stops the motor at the park position and helps prevent it from coasting past the commanded position.<\/p>\n When high-speed operation is requested, the Lighting Control Module also energizes the speed-control relay, routing B+ to the motor\u2019s high-speed circuit.<\/p>\n <\/p>\n\n
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