B101D on GMC: How to Diagnose & Fix

B101D stands for "ECU Hardware (Control Module Internal Hardware Performance)." General Motors body-code definition. When power-up is commanded, the control module runs an internal self-test that requires only battery voltage, ignition voltage and ground; that test runs even when supply voltage is outside the normal operating range. B101D sets when the module detects an internal hardware malfunction during that self-test — the failure is inside the ECU itself, not in an external sensor or actuator. The two-character symptom suffix (e.g. B101D-00, -31, -39, -3B, -F0) narrows which internal element failed. Because this code can be stored by any GM body module, the affected function depends on which module reported it (e.g. a Power Steering Control Module for a lane-keep/steering complaint, a Seat Module for a Safety Alert Seat complaint). On GMC it is documented across 1 model: Terrain.

The most common causes of B101D are: Internal failure of the reporting control module (ECU hardware fault) — the module is normally replaced and programmed, Corrupt or incomplete software/calibration in the module after a failed SPS programming event, Severe under- or over-voltage events, jump-start spikes or a failing battery stressing module internals, Water intrusion or corrosion inside the module housing, Poor power/ground supply to the module causing repeated resets. The specific cause varies by vehicle.

Published repair estimates on GMC range from $100 to $900 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.