GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2007 🢒 Terraza Ext. 🢒 DTC 🢒 DTC B3874

Circuit Description

The body control module (BCM) controls and monitors the state of the wiper control circuit. When the windshield wiper switch is placed in to a low speed setting, a signal is applied to the BCM. The BCM then applies battery positive voltage to the coil side of the WPR1 relay through the WPR1 relay control circuit. This energizes the WPR1 relay, allowing battery positive voltage from the FRT WPR fuse through the switched side of the WPR1 relay to the windshield wiper motor. Ground is applied at all times to the coil side of the WPR1 relay and the windshield wiper motor form G200.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3874 Wiper Low Speed Relay Circuit

Conditions for Running the DTC
    • The ignition is in the ON position.
    • The ignition voltage is between 9-16 volts.

Conditions for Setting the DTC

The following conditions will cause the DTC to set:

    • The BCM detects an short to battery positive voltage in the WPR1 relay control circuit for over 1 second.
    • The BCM detects a short to ground or an open in the WPR1 relay control circuit.

Action Taken When the DTC Sets

The BCM will not activate the output.

Conditions for Clearing the DTC
    • The DTC will clear on current status after the condition for setting the fault is corrected.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • History and current DTCs can be cleared using a scan tool.

Diagnostic Aids

Perform a visual inspection for loose or poor connections at all related components. Refer to Testing for Intermittent Conditions and Poor Connections .

Step

Action

Yes

No

Schematic Reference: Wiper/Washer Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Turn the ignition to the ON position.
  2. On the wiper switch, select a low speed.

Do the windshield wipers operate?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3
  1. Turn the ignition to the OFF position.
  2. Turn the wiper switch OFF.
  3. Remove the WPR1 relay from the underhood fuse block.
  4. Using a test lamp connected to ground, probe the WPR1 relay control circuit at the underhood fuse block.

Does the test lamp illuminate?

Go to Step 8

Go to Step 4

4
  1. Leave the test lamp connected.
  2. Turn the ignition to the ON position.
  3. Turn the wiper switch to a low position.

Does the test lamp illuminate?

Go to Step 5

Go to Step 6

5
  1. Turn the wiper switch to the OFF position.
  2. Turn the ignition to the OFF position.
  3. Using a test lamp, probe the WPR1 relay control circuit and the ground circuit of the WPR1 relay at the underhood fuse block.
  4. Turn the ignition to the ON position.
  5. Turn the wiper switch to a low position.

Does the test lamp illuminate?

Go to Step 9

Go to Step 7

6

Test for a poor connection, an open, or short to ground in the WPR1 relay control circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 10

7

Test for a poor connection or an open in the ground circuit of the WPR1 relay. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 11

8

Repair a short to battery positive voltage in the WPR1 relay control circuit. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

Go to Step 12

--

9
  1. Replace the WPR1 relay. Refer to Relay Replacement .
  2. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 11

Go to Step 12

10

Replace the body control module (BCM). Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 12

--

11

Replace the underhood electrical center. Refer to Underhood Electrical Center or Junction Block Replacement .

Did you complete the replacement?

Go to Step 12

--

12
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions For Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK