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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Corvette 🢒 Body and Accessories 🢒 Theft Deterrent 🢒 DTC B2721

Circuit Description

The body control module (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 theft deterrent relay to energize.
    • The steering column to unlock.
    • The BCM sends a message through the serial data line to the powertrain control module (PCM) to enable fuel delivery.

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

Conditions for Setting the DTC
    • The resistance level sampled at the BCMs PASS-Key® signal circuit is one of 15 valid but incorrect resistance ranges, signaling an invalid PASS-Key® detection.
    • This condition must be present for 1 second.

Action Taken When the DTC Sets
    • The BCM stores DTC B2721 in memory.
    • The BCM sends a message to the instrument panel cluster (IPC) to illuminate the SECURITY indicator.
    • The BCM will disable the theft deterrent 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.
    • The steering column remains in the locked position.

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 after the 3 minute time-out period occurs.
    • A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • Use the IPC clearing DTCs feature.
    • Use a scan tool.

Diagnostic Aids
    • The following conditions may cause an intermittent malfunction:
       - There is an intermittent open or short to ground on the PASS-Key® signal or ground circuit.
       - There are poor connections at the BCM or the ignition switch connector.
       - The ignition lock cylinder key contacts or the PASS-Key® resistor is dirty or loose.
    • If the key resistor pellet is incorrect, there will be no BCM outputs to the theft deterrent relay or to the PCM. 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.

Test Description

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

  1. Tests for other PASS-Key® DTCs stored in the BCM that will cause a DTC B2721 to set. These DTCs must be diagnosed first.

    2.

  2. Tests for an intermittent or incorrect PASS-Key® Resister reading due to an incorrect or malfunctioning ignition key.

Step

Action

Yes

No

Schematic Reference: Theft Deterrent System Schematics

Connector End View Reference: Theft Deterrent System Connector End Views

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 Display DTCs function for the BCM.

Does the scan tool display DTC B2721 as a current DTC?

Go to Step 3

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

3

Does the scan tool display DTC B2722 or B2723 as a current DTC?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4

Inspect the ignition key for dirt or obvious damage.

Does the ignition key appear dirty or damaged?

Go to Step 11

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the ignition lock cylinder.
  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. Turn the rotary switch on the J 35628-A to each code number (1-15) and attempt to start the vehicle with each code number. (After each failed starting attempt, you must wait 3 minutes before the next attempt. This step may take as long as 45 minutes due to a trial and error process.)

Does the vehicle start with one of the codes selected on the J 35628-A ?

Go to Step 6

Go to Step 7

6
  1. Note the code number on the J 35628-A that successfully started the vehicle.
  2. Obtain and cut a new ignition key with the correct key code value.
  3. Attempt to start the vehicle with the new ignition key.

Does the vehicle start?

Go to Step 13

Go to Step 8

7

Test the following circuits for an open or a short:

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

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

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 13

Go to Step 11

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 13

Go to Step 12

10

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

Did you complete the procedure?

Go to Step 13

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11

Replace the ignition lock cylinder. Refer to Ignition Switch Lock Cylinder Replacement in Instrument Panel, Gages, and Console.

Did you complete the replacement?

Go to Step 13

--

12

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 13

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13
  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