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Home >> Buick >> 1997 >> Century Custom >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Body Control Module >> Diagnosis & Repair >> DTC B2721, Pass-Key(R) Detection Circuit (Out Of Range) >> Diagnostic Aids

Diagnostic Aids

  1. The following conditions may cause an intermittent: Intermittent open or short to ground in circuit No. 1073 (Black/White wire) or No. 1074 (Purple/White wire); poor connections; or dirty or loose ignition lock cylinder key contacts or PASS-KEY(R) II resistor.
  2. If key resistor pellet is incorrect, there will be no BCM outputs to theft deterrent relay or PCM for about 3 minutes. If a key (even a proper PASS-KEY(R)) is inserted or ignition is turned on again, 3-minute timeout period will reset. If battery is disconnected, timeout period will be reset when battery is reconnected. During this 3-minute period, the SECURITY warning indicator will flash. After the 3-minute period, SECURITY warning indicator will stay on steady, and BCM will enter the theft deterrent auto-learn mode.
  3. Though it is unlikely, DTC B2721 may set due to extremely hot or cold ambient temperatures. To eliminate this possibility, perform tests with vehicle and key at room temperature.
  4. Clean key resistor contacts thoroughly. Check for poor connections at BCM and ignition lock cylinder. A poor connection may cause an open, an incorrect PASS-KEY(R) resistance or an intermittent malfunction.
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