GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Classic - 2WD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC B3808

Circuit Description

The body control module (BCM) internally grounds the door lock relay control circuit for the rear door lock relay when it receives a class 2 message from the driver door module (DDM) or passenger door module (PDM). When the BCM grounds the door lock relay control circuit the rear door lock relay is energized and locks the rear doors.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3808 Rear Door Lock Relay Circuit

Conditions for Running the DTC
    • Battery voltage is between 9-16  volts.
    • The DTC will set if the rear door lock function is active or inactive.

Conditions for Setting the DTC

The DTC will set if the door lock relay control circuit is shorted to ground or open for more then 1 second.

Action Taken When the DTC Sets
    • If a short to ground is present on the door lock relay control circuit, the door lock relay will be energized and the rear door lock actuators will be held in the lock position and will not unlock.
    • If an open condition is present on the door lock relay control circuit, the rear doors will unlock but not lock.

Conditions for Clearing the DTC

When the fault is no longer present, the BCM changes the current DTC to a history DTC. The BCM will clear the history DTC after 50 fault-free ignition cycles.

Diagnostic Aids
    • DTC B3808 could also set if the door lock relay winding is open.
    • If both DTC B3808 and B3809 are set as current, the battery positive voltage circuit or the LOCKS fuse could be open. If the LOCKS fuse is open, the cause is most likely one of the following:
       - A short to ground in the relay battery positive voltage circuit
       - A short to ground in the door lock actuator lock or unlock control circuits

Test Description

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

  1. Listen for an audible click when the rear door lock relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. This step tests for voltage at the coil side of the rear door lock relay. The LOCKS fuse supplies power to the coil side of the rear door lock relay.

    3.

  3. This step verifies that the BCM is providing ground to the rear door lock relay.

    4.

  4. This step tests if ground is constantly being applied to the rear door lock relay.

Step

Action

Yes

No

Schematic Reference: Door Lock/Indicator Schematics

Connector End View Reference: Vehicle Access Connector End Views

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. With a scan tool, command the rear door lock relay ON and OFF.

Does the rear door lock relay turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Remove the rear door lock relay.
  2. Probe the battery positive voltage circuit of the rear door lock relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 8

4

  1. Connect a test lamp between the door lock relay control circuit and the battery positive voltage circuit of the rear door lock relay.
  2. With a scan tool, command the rear door lock ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 9

Go to Step 5

5

Does the test lamp remain illuminated without being commanded?

Go to Step 7

Go to Step 6

6

Test the door lock relay control circuit of the rear door lock relay for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 10

7

Test the door lock relay control circuit of the rear door lock relay for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 10

8

Test for an open or short to ground in the battery positive voltage circuit of the rear door lock relay. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

Go to Step 14

Go to Step 11

9

Inspect for poor connections at the rear door lock relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 13

11

Repair the short to ground in the door lock actuator lock or unlock circuits. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 14

--

12

Replace the rear door lock relay.

Did you complete the replacement?

Go to Step 14

--

13

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 14

--

14
  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