Wiper/Washer System Description and Operation
Wiper/Washer System Components
The wiper/washer system consists of the following electrical components:
• Windshield Wiper Relay
• Windshield Wiper Speed Control Relay
• Windshield Washer Pump Relay
• Windshield Washer Fluid Pump
• Windshield Wiper Motor
• Window Wiper/Washer Switch
• Windshield Wiper Motor Fuse
• Windshield Washer Fluid Pump Fuse
• Body Control Module (BCM)
• Rear Window Wiper Motor
• Rear Window Wiper Motor Fuse
• Rear Window Wiper Relay
• Rear Window Washer Pump Relay
• Rear Window Washer Pump Fuse
Windshield Wiper System
The body control module (BCM) determines the front wipe/wash system mode of operation by monitoring several signals from the
front wipe/wash switch as indicated in the wiper switch.
The front wipe/wash switch receives a reference ground signal from the BCM. Each input of the BCM provides a switched battery pull
-up for each front wiper/washer switch output signal it receives. All the BCM inputs are recognized as active when the wiper switch
provides a path to the referenced ground signal. The first signal received by the BCM is the result of 6 resistors in the front wiper
switch configured as a resistor ladder network. This signal is connected to a BCM analog to digital input. Depending on the function
selected (High, Low, Intermittent 1 thru 5, Mist, Off), the front 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 wiper motor On/Off Relay. It should be noted that High, Low, and Mist all have the same value on this signal circuit. The
second signal received from the front wiper switch is active only when the front wiper switch is in the high speed wiper position.
When the wiper switch is not in the high speed position, the switch is open and the signal circuit is pulled to battery by the BCM.
When the wiper switch is in the high speed position, the switch pulls the circuit low. The BCM determines how to control the Wiper
high/low speed relay from this input. The third signal received from the front wiper switch is from the momentary windshield wash
control switch. When the washer switch is not active the switch is open and the signal circuit is pulled to battery by the BCM. When
the washer switch is active, the switch pulls the circuit low. The BCM controls the windshield wash and windshield wash activated
wiper operation based on this input.
The BCM controls front wiper motor operation through two output signals and the monitoring of one input signal. The two outputs
(one high side drive, one low side drive) are used to control two external wiper motor relays: front wiper motor on/off relay: which
provides the wiper motor with battery power when it is activated by the high side drive signal (switched battery) from the BCM.
When left deactivated, the normally closed contacts provide a ground to the wiper motor. Wiper high/low speed relay: when
activated by a low side drive signal (ground) from the BCM, it switches the power supplied by the wiper motors on/off relay to the
motors high speed input. When left deactivated, the normally closed contacts connect the power supplied by the wiper motors on/off
relay to the motors low speed input. The input used by the BCM is from the park switch located in the wiper motor assembly. When
the wiper blades are not in the park position, the wiper park switch is open and the circuit is pulled up to battery by the BCM. When
the wiper blades are in the park position at the bottom of the glass, the wiper park switch closes to ground pulling the park signal
circuit low.
To initiate low speed operation, the BCM only energizes the front wiper motor on/off relay. This allows battery voltage from the
wiper fuse to be applied through the switched contacts of the wiper motor on/off relay, through the normally closed contacts of the
wiper high/low speed relay, to the low speed control circuit of the windshield wiper motor.
Redundant high speed switch pass through. The BCM provides redundant circuitry which places battery power on its wiper motor
on/off relay output with activation of its low assertion high speed wiper switch input. The BCM shall be capable of doing this, even if
the module has lost all microprocessor control. This redundant circuit shall supply power while in the RUN and CRANK power modes.
however; while in the CRANK power mode, the pass through shall only be active if the BCM is NOT in a computer operating properly
state.
To initiate high speed operation, the BCM energizes both the front wiper motor on/off relay and the wiper high/low speed relay . This
allows battery voltage from the wiper fuse to be applied through the switched contacts of the wiper motor on/off relay, through the
switched contacts of the wiper high/low speed relay, to the high speed control circuit of the windshield wiper motor.
Parking the wiper motor. In order to perform an accurate read of the park switch and to ensure the wipers will come to rest while
still in the park position, parking of the wipers only occurs while in a low speed wiper mode. This requires that if the wipers are
performing a high speed wiper operation at the time they are required to park, the BCM shall transition the Wipers to low speed by
deactivating the wiper high/low relay before attempting to park. In order to park the wipers, the BCM monitors the park circuit until
the park switch pulls the park circuit to ground. At this time, the BCM will immediately deactivate the wiper motor on/off relay. The
relay contacts will switch back to their normally closed position and will apply ground to the wiper motor power inputs through the
normally closed contacts of the wiper high/low relay. This deactivates and dynamically brakes the wiper motor in the park position.
When the wiper switch is turned to the OFF position while the wiper motor is somewhere in mid-cycle, the BCM will continue to
operate the motor until the wipers reach the park position. If the BCM is running the wiper motor and does not see a state transition
of the park switch after 8 s, the wipers will stop immediately when the wiper switch is turned to OFF. If the ignition is turned OFF
while the wipers are in mid-cycle, the wipers will stop immediately, regardless of position. The BCM will park the wipers next time
the ignition is turned ON.
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 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.
Wipers and Washers
BODY SYSTEMS
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CHEVROLET SONIC 2012 BODY REPAIR MANUAL
