GM Service Manual Online
For 1990-2009 cars only

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 Descriptors

DTC B291A 39: Content Theft Deterrent Assembly Internal Malfunction

Circuit/System Description

This diagnostic applies to internal microprocessor integrity conditions within the content theft deterrent module (intrusion/inclination module).

Conditions for Running the DTC

    • The ignition is OFF.
    • The vehicle is in Park.

Conditions for Setting the DTC

The body control module detects an internal failure within the content theft deterrent module.

Action Taken When the DTC Sets

The intrusion and inclination output is disabled

Conditions for Clearing the DTC

    • A current DTC is cleared when the conditions for setting the DTC are no longer present.
    • A history DTC will clear after 40 malfunction free ignition cycles.

Reference Information

Schematic Reference

Theft Deterrent System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Content Theft Deterrent (CTD) 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 Testing

1. Verify that DTC B291A is not set.

If the DTC is set, replace the A621 content theft deterrent sensor module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Theft Deterrent Module Replacement
    •  Control Module References for body control module replacement, setup, and programming