B2721

DTC B2721

CIRCUIT DESCRIPTION
The body control module (BCM) supplies a 5 volt signal and a ground circuit for the PASS-Key(R) system. This allows the BCM to detect PASS-Key(R) resistance values. Inserting the PASS-Key(R) (with resistor pellet) in the ignition lock cylinder completes the PASS-Key(R) 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(R) signal circuit is one of 15 valid but incorrect resistance ranges, signaling an invalid PASS-Key(R) 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(R) 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(R) resistance value on the PASS-Key(R) 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(R) 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(R) 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

Steps 1 - 4:

Steps 5 - 8:

Steps 9 - 13:

The numbers below refer to the step numbers on the diagnostic table.
3. Tests for other PASS-Key(R) DTCs stored in the BCM that will cause a DTC B2721 to set. These DTCs must be diagnosed first.
4. Tests for an intermittent or incorrect PASS-Key(R) Resister reading due to an incorrect or malfunctioning ignition key.