GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2007 🢒 Lucerne 🢒 DTC 🢒 DTC B2705

Circuit Description

The body control module (BCM) controls the shift lock solenoid by providing battery voltage to the shift lock control solenoid. The BCM utilizes a smart driver to control the voltage supplied to the shift lock solenoid. The smart driver monitors the voltage and current flow of the control circuit.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2705 Gearshift Unlock Circuit

Conditions for Running the DTC
    • The ignition switch is in the ON position.
    • The brake pedal is depressed.
    • The transmission the PARK position.

Conditions for Setting the DTC

The BCM output driver detects an open or short in the output control circuit.

Action Taken When the DTC Sets

The BCM disables the output control until the next ignition cycle.

Conditions for Clearing the DTC
    • A current DTC B2705 will clear when the malfunction is no longer present and the ignition switch is cycled.
    • All BCM history codes will clear after 100 ignition cycles with no current codes active during the 100 ignition cycles.

Diagnostic Aids
    • Use a scan tool to verify there are no brake pedal position sensor and/or transmission internal mode switch (IMS) DTCs set that could cause the BCM not to provide battery voltage to the shift lock control solenoid.
    • If the automatic transmission shift lock solenoid control circuit is shorted to battery positive voltage, the shift lock solenoid will be inoperative. The vehicle will shift out of PARK without depressing the brake pedal, with Floor Shift. On vehicles with Column Shift the shifter will locked in PARK.
    • Perform the tests while wiggling the wires and connectors. This may often cause an intermittent malfunction to appear. Refer to Testing for Intermittent Conditions and Poor Connections .

Test Description

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

  1. Listen for an audible click when the shift lock solenoid operates. Command both the Active and Inactive states. Repeat the commands as necessary.

    2.

  2. This step tests for battery voltage at the control circuit of the shift lock solenoid.

    3.

  3. This step tests for an open or short to ground at the control circuit of the shift lock solenoid.

    4.

  4. This step tests for an open at the ground circuit of the shift lock solenoid.

Step

Action

Yes

No

Schematic Reference: Shift Lock Control Schematics

Connector End View Reference: Shift Lock Control 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. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the shift lock solenoid output control ON and OFF.
  4. With a scan tool, observe the shift lock solenoid command parameter in the body control module (BCM) data list.

Does the shift lock solenoid command display ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the shift lock solenoid.
  3. Connect a test lamp between the shift lock solenoid control circuit at the connector of the shift lock solenoid and a good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, command the shift lock solenoid output control ON and OFF several times.

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

Go to Step 5

Go to Step 4

4

Test the control circuit of the shift lock solenoid for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 10

Go to Step 7

5

Test the shift lock solenoid ground circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 10

Go to Step 6

6

Inspect for poor connections at the harness connector of the shift lock solenoid. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 10

Go to Step 8

7

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

Did you find and correct the condition?

Go to Step 10

Go to Step 9

8

Replace the shift lock solenoid. Refer to Automatic Transmission Shift Lock Control Actuator Replacement for column shift or Transmission Control Replacement for console shift.

Did you complete the replacement?

Go to Step 10

--

9

Important: Perform the set up procedures for the BCM.

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

Did you complete the replacement?

Go to Step 10

--

10
  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