GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Rendezvous - FWD 🢒 Accessories 🢒 Navigation Systems 🢒 DTC B3857

Circuit Description

The body control module (BCM) monitors the high beam headlamp signal circuit by verifying the high beam input.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3857 Headlamp High Beam Signal Circuit

Conditions for Running the DTC
    • Voltage supplied to the module is in the normal operating voltage range, approximately 10-16 volts.
    • The high beam headlamps must be ON.

Conditions for Setting the DTC
    • The BCM detects a short to voltage, short to ground or an open in the high beam headlamp signal circuit.
    • The condition must be present for more than 3 ms.

Action Taken When the DTC Sets
    • The BCM stores DTC B3857 in memory.
    • The SERVICE VEHICLE SOON telltale illuminates.

Conditions for Clearing the DTC
    • A current DTC B3857 will clear if the BCM no longer detects a short to battery voltage, short to ground or an open in the high beam headlamp signal circuit.
    • A history DTC B3857 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • A DTC B3857 will clear when commanded by a scan tool.

Diagnostic Aids
    • If the DTC B3857 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent short to voltage in the high beam headlamp signal circuit.
       - An intermittent short to ground in the high beam headlamp signal circuit.
       - An intermittent open in the high beam headlamp signal circuit.
       - An intermittent short to voltage in the BCM.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for a short to battery positive voltage in the high beam headlamp signal circuit.

    2.

  2. This step tests for a short to ground or an open in the high beam headlamp signal circuit.

Step

Action

Yes

No

Schematic Reference: Headlights/Daytime Running Lights (DRL) 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. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Turn the headlamp switch OFF.
  4. With a scan tool, observe the high beam input data.

Does the scan tool display 0 volts?

Go to Step 3

Go to Step 4

3

  1. Turn the high beam headlamps ON.
  2. With the scan tool, observe the high beam input data.

Does the high beam input parameter change state?

Go to Diagnostic Aids

Go to Step 5

4

Test the high beam circuit for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5

Inspect for a high resistance or a short to ground in the high beam headlamp sensing circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6

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

Did you complete the replacement?

Go to Step 7

--

7
  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