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Tahoe / Yukon Service Manual

DTC B1977

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 Telematics Requested Immobilization For symptom byte information, refer to Symptom Byte List. Circuit/System Description As part of the vehicle telematics enhanced services, a request may be sent to the body control module (BCM) to disable vehicle starting. If a valid message is received by the BCM requesting that starting be disabled, the start enable message will not be sent to the engine control module (ECM). Conditions for Running the DTC The BCM continuously monitors for this DTC. Conditions for Setting the DTC A start disable message has been received from the telematics module. Action Taken When the DTC Sets Vehicle starting will be suspended and the security indicator will be illuminated. Conditions for Clearing the DTC A current DTC will clear when the telematics start disable request is no longer received. A history DTC will clear after 100 ignition cycles in which the telematic start disable request is not seen. Diagnostic Aids DTC B1977 is only an indicator that a start disable request has been received from the vehicle telematics system and does not indicate a fault in the immobilizer or telematics system. To remove the start disable request, the vehicle account must be updated with the OnStar stolen vehicle team. This will require that a law enforcement agency or the customer contact OnStar to indicate that the vehicle has been successfully and safely recovered. If the OnStar system has been disabled or damage during a theft attempt, the system will not be able to communicate and the start disable request will not be removed. OnStar must be functioning properly for the start disable request to be removed. 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 the OnStar system is not damaged and is operating properly, with no DTCs set. ⇒ If the OnStar system is damaged, inoperative, or any OnStar DTCs are set These concerns must be corrected before the start disable can be removed. ⇓ If the OnStar system is not damaged and is operating properly
  2. Press the blue OnStar button and ask the advisor to be transferred to the stolen vehicle team to verify the vehicle account has been updated.
  3. Verify that OnStar is aware the vehicle has been recovered and that the vehicle account has been updated. ⇒ If OnStar has not been notified that the vehicle has been recovered Contact the customer and advise them that for security purposes, they must contact OnStar and the law enforcement agency to update the vehicle account. ⇓ If the account has been properly updated
  4. Once the vehicle account has been updated and the start disable request has been removed, DTC B1977 will transition to a history DTC. Clear the history DTC.