Wiper and Washer Systems: Description and Operation

Wiper/Washer

How the Circuit Works

The wiper/washer system is a multiplex controlled system. The combination switch control unit, MICU, and relay control module are the main operational controls of the wiper/washer system. The washer motor relay, intermittent wiper relay, and windshield wiper high relay are incorporated in the relay control module.

Testing the control unit components and reading Diagnostic Trouble Codes (DTCs) within the multiplex integrated control system can be done by using an HDS Tester. There are more than 80 multiplex system DTCs. The wiper motor and washer motor can still be tested manually without an HDS Tester.

Power Supply
Battery voltage is supplied at all times through fuse 7 (in the under-dash fuse/relay box) to the MICU and combination switch control unit. With the ignition switch in ON (II) or START (III), battery voltage is supplied through fuse 21 (in the under-dash fuse/relay box) to the MICU, the combination switch control unit, and the relay control module. Battery voltage is also supplied through fuse 11 (in the under-dash fuse/relay box) to the windshield wiper motor and through fuse 20 (in the under-dash fuse/relay box) to the windshield washer motor.

Mist
When the wiper/washer switch is moved to MIST the signal for mist is sent to the combination switch control unit. The combination switch control unit communicates that command via a multiplexed signal to the relay control module. The relay control module energizes the intermittent wiper relay supplying ground to the high winding of the windshield wiper motor, causing the motor to run in high. As soon as the motor starts running, the mechanical park/run switch built into the motor will move from PARK to RUN. With the motor running, the mechanical park/run switch is in RUN, sending a ground signal to the relay control module. If the switch is held in MIST for multiple wiper cycles, the PARK/RUN signal will alternate between PARK (battery voltage) and RUN (ground), indicating what position the wipers are in to the relay control module.

Intermittent
When the wiper/washer switch is moved to INTERMITTENT the signal for intermittent and the signal for the intermittent dwell time controller are sent to the combination switch control unit. The combination switch control unit communicates that command via a multiplexed signal to the relay control module. The relay control module energizes the intermittent wiper and windshield wiper high relays, supplying ground to the low winding of the windshield wiper motor and causing the motor to run in low. The relay control module only energizes the intermittent wiper relay long enough to make the motor start running. As soon as the motor starts running, the mechanical park/run switch built into the motor will move from PARK to RUN. With the motor running, the mechanical park/run switch is in RUN, sending a ground signal to the relay control module. If the switch is in INTERMITTENT for multiple wiper cycles, the PARK/RUN signal will alternate between PARK (battery voltage) and RUN (ground), indicating what position the wipers are in to the relay control module.

Low Speed
When the wiper/washer switch is moved to LOW, the signal for low is sent to the combination switch control unit and directly to the relay control module. The combination switch control unit communicates the low signal command via a multiplexed signal to the relay control module. The relay control module energizes the intermittent wiper and windshield wiper high relays, supplying ground to the low winding of the windshield wiper motor and causing the motor to run in low. As soon as the motor starts running, the mechanical park/run switch built in the motor will move from PARK to RUN. With the motor running, the mechanical park/run switch is in RUN, sending a ground signal to the relay control module. If the switch is in LOW for multiple wiper cycles, the PARK/RUN signal will alternate between PARK (battery voltage) and RUN (ground), indicating what position the wipers are in to the relay control module.

When the wiper/washer switch is moved to OFF, the signal for off is sent to the combination switch control unit. The combination switch control unit communicates that command via a multiplexed signal to the relay control module. The relay control module de-energizes the intermittent wiper relay, switching the ground path provided to the low winding of the motor through the RUN contact of the park/run switch. The motor will stop when the wipers reach the PARK position.

High Speed
When the wiper/washer switch is moved to HIGH, the signal for high is sent to the combination switch control unit and directly to the relay control module. The combination switch control unit communicates the high signal command via a multiplexed signal to the relay control module. The relay control module energizes the intermittent wiper relay supplying ground to the high winding of the windshield wiper motor, causing the motor to run in high. As soon as the motor starts running, the mechanical park/run switch built into the motor will move from PARK to RUN. With the motor running, the mechanical park/run switch is in RUN, sending a ground signal to the relay control module. If the switch is in HIGH for multiple wiper cycles, the PARK/RUN signal will alternate between PARK (battery voltage) and RUN (ground), indicating what position the wipers are in to the relay control module.

When the wiper/washer switch is moved to OFF, the signal for off is sent to the combination switch control unit. The combination switch control unit communicates that command via a multiplexed signal to the relay control module. The relay control module de-energizes the intermittent wiper relay, switching the ground path provided to the high winding of the motor through the RUN contact of the park/run switch. The motor will stop when the wipers reach the PARK position.

Washer
When the wiper/washer switch is moved to WASH, the signal for wash is sent to the combination switch control unit. The combination switch control unit communicates that command via a multiplexed signal to the relay control module. The relay control module energizes the washer motor and intermittent wiper relays supplying ground to the windshield washer motor and the high winding of the windshield wiper motor. The windshield washer motor pumps washer fluid onto the windshield, and the windshield wiper motor runs in high. As soon as the wiper motor starts running, the mechanical park/run switch built in the motor will move from PARK to RUN.