GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Century 🢒 DTC 🢒 DTC B2708

Circuit Description

The body control module (BCM) controls the brake to shift relay control circuit and monitors the voltage of the control circuit.

DTC Descriptor

This diagnostic procedure supports the following DTC: DTC B2708 Gearshift Unlock Circuit High

Conditions for Running the DTC

The ignition is in the ON position.

Conditions for Setting the DTC
    • The BCM detects the brake to shift relay control circuit voltage is at or above 8.0 volts in the ON state.
    • The condition above must be present for more than 0.3 seconds.

Action Taken When the DTC Sets

The BCM stores DTC B2708 in memory.

Conditions for Clearing the DTC
    • A current DTC B2708 will clear if the short to voltage in the brake to shift relay control circuit is no longer detected by the BCM or after one ignition cycle.
    • A history DTC B2708 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 DTC B2708 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 voltage in the brake to shift relay control circuit.
       - The brake to shift relay is intermittently shorted to voltage internally.
       - The BCM is intermittently shorted to voltage internally.

Test Description

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

  1. Listen for an audible click when the brake to shift relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. Verifies that the BCM is providing ground to the control circuit of the brake to shift relay.

    3.

  3. Tests if short to battery voltages is present.

    4.

  4. Tests if the brake to shift relay control circuit is open.

    5.

  5. The body control module must be programmed for the vehicle RPO configuration.

Step

Action

Yes

No

Schematic Reference: Shift Lock Control Schematics

Connector End View Reference: Shift Lock Control Connector End Views or Computer/Integrating Systems Connector End Views in Computer/Integrating Systems

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 brake to shift relay ON and OFF.

Does the brake to shift relay turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the brake to shift relay.
  3. Connect a test lamp between the control circuit of the brake to shift relay and brake to shift relay supply voltage circuit at the connector of the brake to shift relay.
  4. Turn ON the ignition, with the engine OFF
  5. With a scan tool, command the brake to shift relay ON and OFF .

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

Go to Step 8

Go to Step 4

4

Does the test lamp remain illuminated?

Go to Step 7

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Connect a test lamp between the control circuit of the brake to shift relay at the body control module (BCM) and battery voltage.
  3. Turn ON the ignition, with the engine OFF
  4. With a scan tool, command the brake to shift relay ON and OFF.

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

Go to Step 6

Go to Step 9

6

Repair the open in the brake to shift relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

--

7

Test the brake to shift relay 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 12

Go to Step 9

8

Inspect for poor connections at the harness connector of the brake to shift relay. 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 12

Go to Step 10

9

Inspect 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 12

Go to Step 11

10

Replace the brake to shift relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 12

--

11

Important: Perform the set-up procedure for the BCM.

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

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