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Home >> Buick >> 2001 >> Century Custom >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Anti-Theft Systems >> Anti-Theft System >> Diagnostic Tests >> DTC B2957: Security System Sensor Data Circuit Low >> Circuit Description

Circuit Description

PASS-Key(R) II detection circuit is completed when ignition key with embedded resistor pellet is inserted in ignition lock cylinder. When contacts in ignition lock cylinder mate with contacts of resistor pellet, key detection circuit through White/Black wire and Purple/White wire is completed.

NOTE: CRANK relay may also be referred to as theft deterrent relay.

When ignition switch is turned from LOCK or OFF position to RUN position, BCM applies a 5-volt reference voltage to White/Black wire. BCM then reads resistor pellet code, and compares stored resistor pellet code with ignition key resistor pellet code to verify a correct match. If BCM determines resistance value of key pellet is correct, BCM will use Class 2 serial data line to send an enable password to PCM. PCM will then energize CRANK relay and allow fuel delivery to engine.

DTC B2957 will set when voltage level of PASS-Key(R) input (White/Black wire) is low (indicating invalid resistance detected or a short to ground) during crank cycle or for one second anytime after engine has been started.

When DTC B2957 is set, BCM will send a message to instrument panel to turn on SECURITY indicator. If DTC is set during crank cycle, BCM will not send a message to PCM to enable CRANK relay and will not allow fuel delivery to engine (vehicle will exhibit a "no crank" condition). If DTC occurs later in ignition cycle, BCM will enter fail-enable mode. During subsequent engine starts, BCM will send a message to PCM to enable CRANK relay and to allow fuel delivery to engine.

A current DTC B2957 will clear from memory when BCM detects a valid PASS-Key(R) resistance value on PASS-Key(R) signal circuit. A history DTC B2957 will clear after 100 consecutive ignition cycles if condition for setting DTC is no longer present. DTC will also clear when scan tool is used to clear DTCs.

NOTE: If DTC B2957 is a history code, problem may be intermittent. Wiggle wires and key while performing following test.
NOTE: When ignition switch is turned to RUN position with BCM disconnected, PCM-related DTC P1626 will be set. After BCM repair is completed, see appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
NOTE: PASS-Key(R) II (VATS) Interrogator (J 35628-A) is required in this procedure.
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