GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Sunfire 🢒 Body 🢒 Doors 🢒 DTC B3127

Circuit Description

The body control module (BCM) controls the driver door lock actuator. The ground is applied to the door lock actuator lock control circuit through the door lock portion of the door lock/unlock relay. When the body control module applies power to the driver door lock actuator unlock control circuit, the door lock actuator energizes and unlocks the door lock.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3127 LF Door Only Unlock Circuit Low

Conditions for Running the DTC

The BCM must be commanding the driver door lock actuator to unlock the door lock. The battery positive voltage supplied to the BCM is within normal operating range of 9-16 volts.

Conditions for Setting the DTC
    • The BCM detects a short to ground in the driver door lock actuator unlock control circuit or the RFA BATT fuse is open while commanding the driver door lock actuator to unlock the door lock.
    • The conditions above must be present for more than 0.3 seconds.

Action Taken When the DTC Sets

The BCM stores DTC B3127 in memory.

Conditions for Clearing the DTC
    • A short to ground in the driver door lock actuator unlock control circuit is no longer detected by the BCM when the BCM is commanding the driver door lock actuator to unlock the door lock.
    • A history DTC B3127 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • A scan tool may be used to clear the DTC.

Diagnostic Aids
    • If the DTC B3127 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent short to ground in the driver door lock actuator unlock control circuit
       - The driver door lock actuator is shorted to ground internally.
       - The BCM is shorted to ground internally.

If the DTC B3127 is accompanied by DTC B3267, the fault may be an open or shorted battery positive voltage circuit, or an open RFA BATT fuse. Refer to Circuit Testing in Wiring Systems.

Test Description

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

  1. Listen for an audible noise when the left front door lock actuator is commanded to unlock. Command the door lock actuator to lock and unlock. Repeat the commands as necessary.

  2. This step verifies that the BCM is providing voltage to the driver door lock actuator.

    3.

  3. This step tests for an open in the door lock actuator lock circuit to the driver door lock actuator.

    4.

  4. This step tests if voltage is constantly being applied to the driver door lock actuator.

Step

Action

Yes

No

Schematic Reference: Door Lock/Indicator Schematics

Connector End View Reference: Power Door Systems Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the driver door unlock relay ON.

Does the driver door lock actuator unlock when commanded?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the driver door lock actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the driver door lock actuator unlock control circuit with a test lamp connected to a good ground.
  5. With a scan tool, command the driver door unlock relay ON.

Does the test lamp flash when the driver door unlock relay is commanded ON?

Go to Step 4

Go to Step 5

4

  1. Connect a test lamp between the driver door lock actuator unlock control circuit and door lock actuator lock control circuit of the driver door lock actuator.
  2. With a scan tool, command the driver door unlock relay ON.

Does the test lamp flash when the driver door unlock relay is commanded ON?

Go to Step 8

Go to Step 10

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test the driver door lock actuator unlock control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the driver door lock actuator unlock control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

Inspect for poor connections at the driver door lock actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

Inspect for an open or short to ground in the battery positive voltage circuit from the RFA BATT fuse to the body control module (BCM) and for poor connections at the harness connector of the body control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair open in the door lock actuator lock control circuit to the driver door lock actuator. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

Replace the driver door lock. Refer to Front Side Door Lock Replacement .

Did you complete the replacement?

Go to Step 13

--

12

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 13

--

13
  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