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Home / DTC / B3903 — Body Control Module Internal Memory Error

B3903 — Body Control Module Internal Memory Error

Detailed page for trouble code B3903.

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B3903

Generic B — Body

Body Control Module Internal Memory Error

Brand: Generic
Type: B — Body
Views: UK: 0 EN: 2 RU: 0
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Page language: EN

Causes

  • Corrupted or failed BCM internal EEPROM/flash memory
  • Interrupted programming or software update (power loss during reflash)
  • Failed internal voltage regulator or power supply to BCM
  • Water intrusion, corrosion, or physical damage to BCM or connector
  • Intermittent wiring, poor ground, or fuse/fusible link issues causing undervoltage
  • Age-related component failure or solder joint failure on BCM board

Symptoms

  • Multiple body electrical faults (door locks, windows, interior lights, wipers)
  • Erratic or non-functional convenience features (remote/keyless, alarm)
  • Instrument cluster warnings or multiple DTCs from other modules
  • Intermittent or complete loss of communication with BCM on CAN
  • Failure to program or inability to retain learned settings
  • Possible no-start or immobilizer-related symptoms when BCM handles security

What to check

  • Record all stored DTCs and freeze-frame data from all modules before clearing
  • Check battery voltage (key off and key on/run); verify charging system
  • Inspect BCM connector for corrosion, bent pins, water entry, and secure mating
  • Check related fuses and fusible links for BCM power and ignition feeds
  • Verify good ground(s) to chassis and BCM ground harness
  • Confirm CAN/serial bus activity and module responses with a scan tool

Signal parameters

  • Battery voltage (key off): ~12.0–12.8 V
  • Battery/charging voltage (engine running): ~13.5–14.8 V
  • Key-on voltage should remain >11.5 V during programming operations
  • CAN bus idle voltages: CAN_H ~2.5 V, CAN_L ~2.5 V (differential ~0 V idle)
  • Module supply rails/internal regulator output (OEM-specific values)
  • EEPROM/flash checksum status: VALID / INVALID (reported by OEM scanner)

Diagnostic algorithm

  1. Capture all stored codes and related module data with a capable OEM or advanced scan tool (record software part numbers, VIN and freeze frame if present).
  2. Verify vehicle battery state-of-charge and charging system. Recharge or replace weak battery before further tests.
  3. Visually inspect BCM housing and connector for water, corrosion, damage, or signs of overheating. Repair or replace damaged harness/connector as needed.
  4. Check BCM power and ground circuits at the connector for proper voltage and continuity. Repair any wiring or fuse faults.
  5. Verify CAN bus health: check for correct bus voltages, termination resistance, and that other modules can communicate. Repair bus wiring faults.
  6. Using OEM scanner, read BCM internal memory status (EEPROM/flash checksum, self-test results) and attempt to clear the code. If code does not return, monitor vehicle for intermittent issues.
  7. If the scanner shows corrupted software or failed checksum, attempt reprogramming/ reflashing with the latest OEM calibration following manufacturer procedures. Ensure stable power (battery charger) during reflash.
  8. If reflash fails repeatedly or internal memory tests fail, consider repair or replacement of BCM. If replacement is required, program/encode new module with vehicle-specific data (VIN, immobilizer keys, body options) per OEM procedure.
  9. After repair or module replacement, clear codes, perform relearns/configuration steps, and verify all body functions and communications. Road test to confirm resolution.
  10. If fault persists after replacement and programming, escalate to manufacturer technical support for known issues or board-level diagnostics.

Likely causes

  • EEPROM/flash checksum mismatch due to corruption
  • Failed internal power regulator or supply rail inside BCM
  • Failed solder joint or physical damage to BCM PCB
  • Vehicle battery/charging problems that occurred during module flash
  • Water or corrosion causing memory or connector failure

Fault status

⚠️ Status
Current/Active fault. BCM reported internal memory error (EEPROM/flash checksum failure or corruption). May require reflash or module replacement if memory cannot be restored.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours

Similar codes

B3900 B3901 B3902 B3910 U0100 U0121
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