B3999

Code

Generic B — Body

Body Control Module — Manufacturer-Specific/Undefined Fault

Brand: Generic

Type: B — Body

Views: UK: 13 EN: 21 RU: 16

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One or more body electrical functions operating intermittently or incorrectly (locks, lights, wipers, mirrors)
Instrument cluster or infotainment may show BCM-related warnings or ‘Service Body Control Module’ message
Keyless entry, alarm, or immobilizer faults
Exterior or interior lights stuck on or not working
Parasite battery drain or BCM not going to sleep
Multiple unrelated codes present from other modules

Connect a capable scan tool. Read all stored and pending DTCs and freeze frame data from BCM and other modules.
Verify battery voltage (12.6 V+ at rest, >13.5 V when charging); check battery state and charging system.
Inspect BCM and harness connectors for corrosion, water, bent pins, or physical damage.
Check main BCM power and ground circuits for continuity and proper voltage under load.
Check CAN/LIN network status: ensure proper termination, measure CAN High/Low voltages with key on and engine off.
Review service information and TSBs for manufacturer-specific notes and required calibrations.

BCM supply voltage (V) at pin(s) B+
BCM ground resistance/continuity (ohms)
CAN High / CAN Low idle voltages (~2.5 V nominal, differential ~0 V idle, ~2.5 V/1.5 V pair depending on system)
LIN bus voltage levels where applicable
Wake/sleep request signal state (ignition, door, key fob inputs)
Status of relevant input switches (door, hood, brake) as seen on scan tool

Capture and save the complete scan tool report (all modules). Note freeze frame and count of occurrences.
Verify battery condition and charging system. If battery weak or charging poor, restore proper battery condition and retest.
Inspect BCM connectors and wiring for corrosion, water intrusion, bent pins, or damage. Repair as needed.
Check and repair all BCM power and ground circuits. Confirm stable voltage to the BCM with loads applied.
Check vehicle network communications: use a scope or scan tool to verify CAN/LIN frames and error counters. Repair wiring/terminations if bus errors present.
Remove/fix any suspected aftermarket devices and clear codes. Recreate conditions to see if code returns.
Check for available software updates or reprogramming procedures from the manufacturer; reflash BCM calibration if recommended.
If code persists after wiring, power, ground, and software verified, follow module replacement procedure per manufacturer, ensuring correct part number and programming/encoding.
After repair or reprogramming, clear codes and perform full system functional test including long-term monitoring for recurrence.

Battery voltage drops or poor battery/charging system causing BCM reset or error
Damaged or corroded connector pins at the BCM
Faulty ground strap or poor chassis ground near BCM
CAN bus short to battery or ground, high bus error rate
Recent aftermarket remote start, alarm or lighting installation
Out-of-date or corrupted BCM software/calibration