GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2004 🢒 Regal 🢒 Accessories 🢒 Theft Deterrent 🢒 DTC B2957

Circuit Description

The BCM supplies a 5 volt signal and a ground circuit for the PASS-Key® system. This allows the BCM to detect PASS-Key® resistance values. Inserting the PASS-Key® (with resistor pellet) in the ignition lock cylinder completes the PASS-Key® circuit. Contacts in the ignition lock cylinder mate with the pellet contacts. The BCM compares the resistance value of the key pellet to the valid resistance programmed into the BCM. If the proper resistance value is read, the BCM allows the following functions to occur:

    • The crank relay to energize.
    • The BCM sends a message through the serial data line to the PCM to allow fuel delivery to occur.

If the resistance value is incorrect, a malfunction is present and a DTC will set.

Conditions for Setting the DTC
    • The voltage level sampled at the BCMs PASS-Key® signal circuit is incorrect, signaling that an invalid PASS-Key® resistance was detected and a short is present.
    • This condition must be present for 1 second.

Action Taken When the DTC Sets
    • The BCM sends a message to the instrument cluster to illuminate the SECURITY indicator.
    • The PCM disables the crank relay.
    • The PCM will not allow fuel delivery to occur.
    • The BCM disables sampling of the PASS-Key® resistance for a time-out period of 3 minutes.

Conditions for Clearing the DTC
    • This DTC requires an ignition cycle in order to change from current to history.
    • The BCM detects a valid PASS-Key® resistance value on the PASS-Key® signal circuit.
    • A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • Use a scan tool.

Diagnostic Aids
    • If the key resistor pellet is incorrect, there will be no outputs to the crank relay or to the PCM fuel delivery system. This state will last about 3 minutes. If a key is inserted, or the ignition is turned ON again before the 3 minute time frame is complete, the timer will reset to 3 minutes. Disconnecting the battery will not clear the timer sequence, but the timer will reset to 3 minutes when the battery power is restored. Even if a proper key is inserted during one of the time periods, the vehicle will not start until the total time period has elapsed.
    • If there is a short between the PASS-Key® signal and ground circuit, or a short to ground on the PASS-Key® signal circuit, the vehicle will exhibit a no crank condition.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This test verifies the integrity of the key resistor circuits between the ignition switch and the BCM.

Step

Action

Yes

No

Schematic Reference: Theft Deterrent System Schematics

1

Did you perform the Theft Deterrent Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Theft Deterrent

2
  1. Install a scan tool.
  2. Turn ON the ignition with the engine OFF.
  3. Select the BCM Display DTCs function on the scan tool.

Does the scan tool display B2957 as a current DTC?

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3

Inspect the ignition key for dirt or obvious damage.

Does the ignition key appear dirty or damaged?

Go to Step 8

Go to Step 4

4

  1. Turn off the ignition.
  2. Disconnect the ignition lock cylinder connector.
  3. Connect a J 35628-A Vats/Passkey Interrogator using terminal adapters from a J 35616 to the key resistor input circuit and key resistor reference ground circuit.
  4. Insert the ignition key into the key code reader on the J 35628-A and note the code on the LCD display.
  5. Turn the rotary switch on the J 35628-A to the same code number as the ignition key.
  6. Attempt to start the vehicle.

Does the vehicle start?

Go to Step 7

Go to Step 5

5

Test the following circuits for a short to ground:

    • The key resistor input circuit
    • The key resistor reference ground circuit

Was a condition found and corrected?

Go to Step 11

Go to Step 6

6

Inspect for poor connections at the harness connector of the BCM. 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 11

Go to Step 10

7

Inspect for poor connections at the harness connector of the ignition lock cylinder. 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 11

Go to Step 9

8

Clean or replace the ignition key as necessary. Refer to Replacing Keys .

Did you complete the procedure?

Go to Step 11

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9

Replace the ignition lock cylinder. Refer to Ignition Lock Cylinder Replacement in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 11

--

10

Important: When replacing the BCM, perform the relearn procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration in Body Control System.

Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the repair?

Go to Step 11

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11
  1. Use the scan tool in order to clear the DTCs.
  2. Attempt to start the vehicle.

Does the DTC reset?

Go to Step 2

System OK