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Chevrolet Silverado / GMC Sierra. Manual - part 3007
Circuit/System Description
The body control module (BCM) controls the wiper motor based on input from the windshield
wiper washer switch. The BCM monitors the wiper washer switch through three separate signal
circuits and a ground circuit. The windshield wiper switch high signal circuit is used to determine
high speed wiper operation, the windshield wiper switch low signal is used to determine low
speed, intermittent, and mist operation through the use of a resistor ladder, and windshield washer
switch signal circuit is used to determine washer operation.
The BCM controls the windshield wiper motor through two output controls, controlling two
relays which determine the desired wiper speed, high or low.
Reference Information
Schematic Reference
Wiper/Washer Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Wiper/Washer System Description and Operation
Electrical Information Reference
Circuit Testing
Connector Repairs
Testing for Intermittent Conditions and Poor Connections
Wiring Repairs
Scan Tool Reference
Ground
1. Delay or Low Speed Wipers Inoperative
2. High Speed Wipers Inoperative
3. Wipers Do Not Park
4. Wipers Always ON
2008 Chevrolet Silverado 1500
2008 ACCESSORIES & EQUIPMENT Wipers and Washers - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
Control Module References for scan tool information
Circuit/System Verification
1. Observe the scan tool Windshield Wiper Switch parameter while rotating the wiper switch.
The reading should change between Off, Intermittent, Low, and High.
If the Windshield Wiper Switch parameter is incorrect in the Low or High switch
positions, refer to the Multifunction Switch Circuit Test and/or the Turn Signal
Multifunction Switch Component Test below.
2. Observe the scan tool BCM Wiper Park Switch parameter. The reading should display
Active when the wipers are parked and Inactive with the wipers ON or out of the park
position.
If the Wiper Park Switch parameter is always Active or Inactive, refer to Wipers do
not Park Circuit Test below.
3. Connect a test lamp between the TP 1 terminal in the underhood fuse block and ground.
4. Verify the test lamp turns on and off while turning the windshield wiper switch between
LOW and OFF.
If the test lamp does not turn on and off while changing between the commanded
states, refer to Wiper Control Relay Control Circuit Test below.
5. Ignition ON, operate the windshield wiper switch through the Delay, Low, and High
positions.
If the windshield wipers are inoperative in 1 or more of the delay settings only, test or
replace the turn signal multifunction switch.
If the windshield wipers operate at high speed while the switch is in the Low position,
refer to Wiper Speed Relay Control Circuit Test below.
If the windshield wipers operate at low speed while the switch is in the High position,
refer to Wiper Speed Relay Control Circuit Test below.
If the windshield wipers are inoperative in the Low or High switch positions, refer to
Wiper Motor Circuit Test and/or the Wiper Motor Component Test below.
Circuit/System Testing
Multifunction Switch Circuit Test
1. Ignition OFF, disconnect the X3 harness connector at the turn signal multifunction switch.
2. Ignition OFF, test for less than 20 ohms between the low reference circuit terminal M and
ground.
If greater than the specified range, test the low reference circuit for an open/high
2008 Chevrolet Silverado 1500
2008 ACCESSORIES & EQUIPMENT Wipers and Washers - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
resistance. If the circuit tests normal, replace the BCM.
3. Verify the scan tool Windshield Wiper Switch parameter is Off.
If not the specified value, test the signal circuit terminal N for a short to ground. If the
circuit tests normal, replace the BCM.
4. Verify the scan tool Wiper High Speed Switch parameter is Inactive.
If not the specified value, test the signal circuit terminal K for a short to ground. If the
circuit tests normal, replace the BCM.
5. Install a 3-amp fused jumper wire between the signal circuit terminal N and ground. Verify
the scan tool Windshield Wiper Switch parameter is Switch Fault.
If not the specified value, test the signal circuit for a short to voltage or an open/high
resistance. If the circuit tests normal, replace the BCM.
6. Install a 3-amp fused jumper wire between the signal circuit terminal K and ground. Verify
the scan tool Wiper High Speed Switch parameter is Active.
If not the specified value, test the signal circuit for a short to voltage or an open/high
resistance. If the circuit tests normal, replace the BCM.
7. If all circuits test normal, replace the turn signal multifunction switch.
Wipers Do Not Park Circuit Test
1. Ignition OFF, disconnect the harness connector at the windshield wiper motor.
2. Ignition ON, verify the scan tool BCM Wiper Park Switch parameter is Inactive.
If not the specified value, test the signal circuit terminal 3 for a short to ground. If the
circuit tests normal, replace the BCM.
3. Install a 3-amp fused jumper wire between the signal circuit terminal 3 and ground. Verify
the scan tool Wiper Park Switch parameter is Active.
If not the specified value, test the signal circuit for an open/high resistance. If the
circuit tests normal, replace the BCM.
4. If all circuits test normal, replace the windshield wiper motor.
Wiper Control Relay Control Circuit Test
1. Ignition OFF, disconnect the X5 harness connector at the BCM.
2. Ignition ON, verify that the low speed wipers are not on.
If the low speed wipers are on, test the relay control circuit terminal 20 for a short to
voltage. If the circuit tests normal, replace the underhood fuse block.
3. Install a 10A fused jumper wire between B+ and the relay control circuit terminal 20.
2008 Chevrolet Silverado 1500
2008 ACCESSORIES & EQUIPMENT Wipers and Washers - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
Verify the low speed wipers are on.
If the low speed wipers are not on, test the relay control circuit for an open/high
resistance or short to ground. If the circuit tests normal replace the underhood fuse
block.
4. If all circuits test normal, replace the BCM.
Wiper Speed Relay Control Circuit Test
1. Ignition OFF, disconnect the X5 harness connector at the BCM.
2. Install a 10A fused jumper wire between B+ and the WIPER CONTROL relay control
circuit terminal 20.
3. Ignition ON, verify that the high speed wipers are not on.
If the high speed wipers are on, test the WIPER SPEED relay control circuit terminal
21 for a short to ground. If the circuit tests normal, replace the underhood fuse block.
4. Install a 10A fused jumper wire between the WIPER SPEED relay control circuit terminal
21 and ground. Verify the high speed wipers are on.
If the high speed wipers are not on, test the relay control circuit for an open/high
resistance or short to voltage. If the circuit tests normal replace the underhood fuse
block.
5. If all circuits test normal, replace the BCM.
Wiper Motor Circuit Test
1. Disconnect the harness connector at the windshield wiper motor.
2. Test for less that 1 ohm between the wiper motor ground circuit terminal 5 and ground.
If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the low speed motor control circuit terminal 1 and ground.
4. Ignition ON, command the Wiper Relay ON and OFF with a scan tool. The test lamp should
turn ON and OFF when changing between the commanded states.
If the test lamp is always ON, test the control circuit for a short to voltage. If the
circuit tests normal, replace the underhood fuse block.
If the test lamp is always OFF, test the control circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the underhood fuse block.
5. Connect a test lamp between the high speed motor control circuit terminal 4 and ground.
6. Wiper switch in the LOW position, command the Wiper High Speed Relay ON and OFF
with a scan tool. The test lamp should turn ON and OFF when changing between the
commanded states.
2008 Chevrolet Silverado 1500
2008 ACCESSORIES & EQUIPMENT Wipers and Washers - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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