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Tahoe / Yukon Service Manual

DTC B1987

Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptor Environment Identification For symptom byte information, refer to Symptom Byte List. Circuit/System Description When certain modules are programmed and configured during installation, the module learns a specific environment identifier which is unique to the vehicle. The environment identifier is used to prevent the swapping modules between vehicles. The body control module (BCM) is the keeper of the environment identifier. The Instrument Cluster, Electronic Brake Control Module, HVAC Control Module, Inflatable Restraint Sensing and Diagnostic Module, engine control module (ECM), and Steering Column Lock Module (if equipped) each learn the environment identifier during their configuration process. During vehicle operation, the BCM sends the immobilizer identifier as a challenge and each module responds to the challenge by sending the environment identifier back to the BCM. If the BCM sends an incorrect immobilizer identifier or a specific number of incorrect environment identifiers are received, vehicle starting is disabled. Conditions for Running the DTC Ignition is in the ACCESSORY or RUN position. Conditions for Setting the DTC An incorrect immobilizer identifier was broadcast by the BCM. Action Taken When the DTC Sets The security indicator in the instrument cluster will illuminate. Vehicle starting will be disabled. Conditions for Clearing the DTC A current DTC will be cleared when the BCM broadcasts a correct immobilizer identifier. Diagnostic Aids If BCM programming is not completed after BCM replacement, the immobilizer identifier will not be learned. If DTC B389A sets immediately after the replacement and programming of a BCM, perform the programming procedure again. Reference Information Schematic Reference Immobilizer Schematics Connector End View Reference Master Electrical Component List Description and Operation Immobilizer Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Circuit/System Verification

  1. Verify DTC B1987 did not set immediately following the replacement and programming of the K9 Body Control Module. ⇒ If the DTC set immediately after the replacement and programming of the K9 Body Control Module The immobilizer learn procedure was not properly completed. Perform the BCM immobilizer learn using the body control module IMMO Function with Existing Transponder or Remote Key in SPS. Refer to Immobilizer System Component Programming. ⇓ If the DTC did not set immediately after the replacement and programming of the K9 Body Control Module
  2. Verify DTC B1987 is not set in any of the control modules listed below: K20 Engine Control Module K36 Inflatable Restraint Sensing and Diagnostic Module K17 Electronic Brake Control Module K33 HVAC Control Module P16 Instrument Cluster K60 Steering Column Lock Module (if equipped) ⇒ If DTC B198A is set in any of the modules Refer to DTC B198A. ⇓ If DTC B198A is not set in any of the modules
  3. Perform the K9 Body Control Module immobilizer learn using body control module IMMO Function with Existing Transponder or Remote Key in SPS. Refer to Immobilizer System Component Programming.
  4. Verify DTC B1987 does not set after programming. ⇒ If the DTC sets after programming Replace the K9 Body Control Module. ⇓ If the DTC does not set after programming
  5. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Control Module References for body control module replacement, programming, and setup.