B29DE

Code

Generic B — Body

Body Control Module Internal Fault

Brand: Generic

Type: B — Body

Views: UK: 11 EN: 8 RU: 9

AI status

Completed

ready

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Page language: EN

Causes

BCM internal hardware failure (processor, memory, I/O)
Corrupted BCM software or firmware
Loss or intermittent battery supply to BCM (poor battery/charger/ignition feed)
Poor or high-resistance ground(s) at BCM
Water/moisture ingress or physical damage to BCM or connector
Faults or short/open on CAN/LIN network wiring to BCM

Symptoms

BCM warning/instrument cluster message (BCM fault)
Multiple body electrical items fail or behave erratically (lighting, locks, windows, wipers)
Loss of communication with the BCM on a scan tool
Intermittent or permanent failure of convenience features
Vehicle may show related U‑codes (communication errors)
Possible no-start or immobilizer-related faults if BCM handles security functions

What to check

Read all stored DTCs and freeze frame data from BCM and other modules
Check for additional U‑codes (communication faults) on the vehicle network
Visually inspect BCM and connectors for corrosion, water entry, damage, rodent chewing
Verify battery state-of-charge and charging system output
Check BCM power and ground pins for presence and quality (voltage, continuity)
Inspect CAN/LIN wiring for shorts, opens, or damaged shielding; check termination resistors

Signal parameters

Battery voltage (engine off): 12.0–12.8 V typical; with engine running: 13.5–14.8 V
BCM primary supply pin: same as battery/ignition feed within 11–15 V range under normal conditions
Ground resistance to chassis:
CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V; dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈2 V)
LIN bus idle: pulled to battery voltage via pull-up (approx. battery voltage) on many systems
Wake/sleep current: expected low quiescent current (varies by vehicle); unexpected high current indicates internal fault or parasitic draw

Diagnostic algorithm

Connect OEM-level scan tool, record DTCs and freeze frame; note related U‑codes and module communication status.
Verify battery voltage and charging system. Charge or replace battery if voltage low; retest for code persistence.
Visually inspect BCM enclosure and connector for water, corrosion, damage; dry/clean if found and retest.
With key on, measure BCM supply and ground pins for proper voltage and low resistance ground. Repair any wiring or fuse faults.
Check CAN/LIN network: measure voltages, use scope if available to view bus signals; verify termination resistors and continuity to other modules.
If communication is intermittent, wiggle test harness and connectors while monitoring communications to locate intermittent connection.
Attempt to clear codes and re-run self-tests. If code returns immediately and all electrical parameters are good, attempt a controlled BCM reboot via OEM tool.
Check for available BCM software/firmware updates and apply reflash per manufacturer procedure; some internal faults clear after a successful reflash.
If BCM fails internal self-tests after power/ground and network verified and reflashing unsuccessful, prepare for BCM replacement; ensure programming/coding tools and immobilizer re‑learn procedures are available.
After replacement or reprogramming, verify all body functions and clear codes; perform road test and re-scan for related network errors.

Likely causes

Corrupted firmware or failed internal memory
Low or intermittent supply voltage to the BCM (battery/ignition feed)
Bad ground(s) at the BCM
Moisture or physical damage to the module or connector
CAN bus noise or loss of communications causing internal fault handling

Fault status

⚠️ Status

Body Control Module has reported an internal fault. The module may be malfunctioning due to hardware, software, power/ground, or network issues. Further electrical diagnostics and possible reprogramming or replacement are required.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 1.5-3.5 hours