B2721

DTC B2721 Pass-Key (R) II Detention Circuit Out Of Range:

DTC B2721 Pass-Key (R) II Detection Circuit Out Of Range (Part 1 Of 2):

DTC B2721 Pass-Key (R) II Detection Circuit Out Of Range (Part 2 Of 2):

CIRCUIT DESCRIPTION
The Personal Automotive Security System (PASS-Key(R) II) is a vehicle theft deterrent system. The PASS-Key(R) II is designed to prevent vehicle theft by disabling the engine from starting unless an ignition key with a specific resistor pellet code is used in the ignition lock cylinder.

The ignition lock cylinder contains the resistor sensing contacts. These contacts touch the resistor pellet embedded in the ignition key. When the ignition key is inserted in the ignition lock cylinder, the resistor pellet completes the key detection circuit (circuits 1073 and 1074).

When the ignition switch is turned from the LOCK or OFF to the RUN position, the Body Control Module (BCM) applies a 5V reference voltage to circuit 1073. Then, the BCM reads the resistor pellet code and compares the stored resistor pellet code against the ignition key resistor pellet code for a correct match.

Upon detecting a correct match, the BCM sends a fuel enable password to the Powertrain Control Module (PCM) through the Class II serial data link. As a result, the PCM enables the theft deterrent relay, and allows fuel delivery to the engine.

CONDITIONS FOR SETTING THE DTC
^ The resistance detected in circuit 1073 by the BCM is one of 14 valid but incorrect PASS-Key(R) II resistance ranges; signalling an invalid resistor pellet code match.
^ Condition must be present during an engine start attempt, or for 1 second anytime after the engine has started.

ACTION TAKEN WHEN THE DTC SETS
The BCM takes one of two actions:
1. If the PASS-Key(R) II resistance is out of range when attempting to start the vehicle, then the BCM:
^ The BCM stores DTC B2721 in memory.
^ The BCM sends a message to the Instrument Panel Cluster (IPC) to flash the SECURITY indicator through the Class II serial data link.
^ The BCM sends a message to the PCM via Class II serial data link to disable the theft deterrent relay, and to stop fuel delivery to the engine.
^ The BCM disables sampling of the PASS-Key(R) II resistance for a time-out period of 3 minutes.
^ If the ignition switch is left in the RUN position for at least 3 minutes, the BCM enters the theft deterrent re-learn mode. Refer to Theft Deterrent Re-Learn under Repair Instructions for service procedure, OR
2. If the PASS-Key(R) II resistance is initially the proper resistance (and the engine starts), but later on (during the same ignition cycle) the PASS-Key(R) II resistance is out of range, then:
^ The BCM stores DTC B2721 in memory.
^ The BCM enters fail-enable mode.
^ The BCM sends a message to the Instrument Panel Cluster (IPC) to turn on the SECURITY indicator through the Class II serial data link.
^ Upon subsequent engine start attempts, the BCM will send a message to the PCM via Class II serial data link to enable the theft deterrent relay, and to deliver fuel to the engine.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC B2721 will clear when the BCM detects a valid PASS-Key(R) II resistance value on the PASS-Key(R) II input circuit (circuit 1073).
^ A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
^ Using a scan tool.

DIAGNOSTIC AIDS
^ The following conditions may cause an intermittent malfunction to occur:
- Dirty or loose ignition cylinder key contacts. Dirty key resistor pellet.
- Incorrect PASS-Key(R) II.
- An intermittent open or short to ground in circuit 1073 or circuit 1074.
- Poor connections at the BCM or ignition switch connector.
^ If the key resistor pellet is incorrect there will be no communication from the BCM to the PCM to enable the theft deterrent relay, and to enable fuel delivery to the engine. This vehicle disable period state will last approximately 3 minutes during which time the SECURITY indicator will flash when the ignition switch in the RUN position. Disconnecting the battery will not clear the timer sequence, it will resume when battery power is restored. Even if a proper key is inserted during the vehicle disable period, the vehicle will not start until the 3 minute time period has elapsed. After this 3 minute time period, the SECURITY indicator will change from a flashing state to a solid on state. At this time, the BCM enters the theft deterrent re-learn mode. Also, the engine will start if the correct ignition key resistor pellet is used.
^ While very unlikely, it is possible that extremely hot or cold ambient conditions may cause a DTC B2721. To eliminate this possibility, make sure both the vehicle and especially the key are near normal room temperature conditions during testing. Make sure the key resistor contacts are clean and free of any grease, oil, etc. These substances could interfere with the key detection circuit and set this DTC.
^ Check for poor connections at both the BCM and the ignition lock cylinder assembly, these could cause an open, incorrect PASS-Key(R) II resistance, or intermittent malfunction. If the DTC is a history DTC, the problem may be intermittent. Try performing the tests shown while moving wiring, connectors, and the key, this can often cause the malfunction to appear.
^ DTC B2723 may set in the BCM when the ignition switch is in the RUN position with the steering column lock and ignition key cylinder connector (C207) disconnected. When BCM diagnostics and repairs are completed for DTC B2721, clear BCM DTCs and perform the BCM Diagnostic System Check.
^ DTC P1626 will set in the Powertrain Control Module (PCM) when the ignition switch is in the RUN position with the BCM disconnected. When BCM diagnostics and repairs are completed, refer to the Engine Controls for additional information on PCM related DTCs. Powertrain Management

TEST DESCRIPTION
Numbers below refer to the step numbers on the diagnostic table.
2. Checks if the ignition keys supplied with the vehicle are within the allowable range.
3. If certain BCM DTCs are present, perform the diagnostic tables for these DTCs first. The malfunction that caused these other DTCs to set could also set DTC B2721.
4. Determines if the ignition lock cylinder is functioning properly.
5. Checks for a faulty BCM.
6. Determines if one of the ignition keys is faulty.