B3901

Code

Generic B — Body

Body Control Module — Internal Software Error

Brand: Generic

Type: B — Body

Views: UK: 4 EN: 9 RU: 5

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Corrupted or incomplete software/flash image
Interrupted or failed module reprogramming
Low battery or unstable power during programming
Internal memory (flash/NVRAM) or processor fault
Software calibration mismatch after module swap
Loss of power or supply/ground faults to BCM

Symptoms

BCM not responding to scan tool or limited/partial response
Erratic or nonfunctional body functions (lights, locks, windows, wipers)
Multiple body/system DTCs or communication faults present
Instrument cluster or dash warnings related to BCM or communications
Stored U‑codes (CAN/comm) alongside B3901
Vehicle may not retain settings or has unusual behavior after power cycle

What to check

Read freeze frame and full DTC list from BCM and other modules; note timestamps and related U/P codes
Verify battery state of charge and system voltage (preferably 12.4–12.8 V or manufacturer spec)
Inspect BCM connectors, pins, and harness for corrosion, water, or damage
Check BCM power and ground circuits for proper voltage and continuity
Scan CAN/LIN bus for bus‑off, error counters, or other modules losing communication
Attempt to read BCM part number, software/calibration IDs and boot status via OEM scan tool

Signal parameters

Battery voltage at BCM (key on and during cranking)
BCM supply and ground continuity/resistance
CAN High/Low bus activity and error counters
BCM module response codes, software/calibration part numbers, boot status/uptime
Number and type of stored fault codes (BCM and related modules)
Programming status flags or KAM (keep alive memory) errors if available

Diagnostic algorithm

Connect a capable OEM or professional scan tool and retrieve all stored and pending codes from BCM and other modules; save reports
Record freeze frame data and note vehicle voltage during events
Verify battery charge and health; if low, charge and retest (do not program if battery is low)
Visually inspect BCM enclosure and connector for corrosion, water ingress, or physical damage; repair as needed
Verify BCM power and ground circuits (voltage with key on, engine off, and continuity to chassis ground)
Check CAN bus integrity: measure CAN differential voltages, verify termination resistors and that other modules can communicate
Clear codes and perform a controlled power cycle; see if B3901 returns and whether it is intermittent
If hardware and bus are good and software/cal IDs are accessible, check OEM for software updates/TSBs or reprogramming procedures
Attempt to reflash/reprogram the BCM with the correct factory calibration using OEM tool and stable power source (follow OEM precautions — battery charger, maintained voltage)
If reprogramming fails or module will not accept correct software, consider BCM replacement and ensure correct pairing/immobilizer coding if required
After repair/reprogramming, clear codes, reinitialize vehicle settings, and perform full systems communication check and a road test to verify functions remain stable

Likely causes

Recent BCM reflash or dealership/aftermarket programming interrupted
Low battery voltage during a previous update or battery replacement
Failed internal flash memory or worn NVRAM cells
Loose/poor power or ground connection to BCM
Incompatible software loaded to the module
Repeated CAN bus errors or bus-off condition preventing normal initialization

Fault status

⚠️ Status

BCM detected internal software/flash error or failed self‑test; module may be unresponsive or running in fallback mode. Reprogramming or module replacement likely required after verifying power, grounds and CAN network.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 2.0-4.0 hours

Similar codes

Your experience will help others

+100 karma for a short comment :)

Was this AI description helpful?

Your feedback helps improve AI descriptions.

👍 Like 0 👎 Dislike 0

Send to email