B0240

Code

Generic B — Body

Body Control Module — Internal Fault

Brand: Generic

Type: B — Body

Views: UK: 17 EN: 16 RU: 18

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Internal BCM hardware failure (processor, memory, power regulator)
Corrupted or failed BCM firmware/software
Low or unstable battery/vehicle voltage during key events
Poor power/ground connections or blown BCM fuse/relay
Water intrusion, contamination, or physical damage to BCM module or connector
CAN/LIN bus short or severe network errors causing the BCM to enter fail-safe

Symptoms

BCM-related functions inoperative or intermittent (interior/exterior lights, door locks, windows, wipers)
Multiple related DTCs or communication/storage errors present
Instrument cluster or other modules report loss of communication with BCM
Unintended behavior of body systems (random relays, lights on/off)
Possible parasitic battery drain or no-crank depending on vehicle integration

What to check

Read all stored and pending DTCs and freeze-frame data with a capable scan tool
Verify battery voltage and state of charge (preferably 12.4–12.8 V at rest)
Check and verify BCM power and ground circuits, fuses and relays for continuity
Inspect BCM connector and harness for corrosion, bent pins, water damage or signs of overheating
Scan the network for communication errors (U-codes), bus-off conditions, or high error counts
Attempt to clear codes and see if B0240 returns immediately or after specific events

Signal parameters

Battery supply to BCM: ~12 V resting, 13.5–14.8 V with engine running (when applicable)
Ignition-switched supply present when key ON: ~12 V
Ground resistance:
CAN bus idle voltages: CAN_H ~2.5 V, CAN_L ~2.5 V (differential ~0 V idle); active differential pulses during activity
LIN bus idle voltages typically ~12 V or as specified for vehicle; watch for missing wake-up frames
BCM internal wake/sleep currents (refer to service manual) — abnormal high current may indicate internal fault

Diagnostic algorithm

Record freeze-frame and all active/pending DTCs. Note sequence and related modules reporting errors.
Verify and record battery voltage and charging system voltage. Ensure battery is fully charged or use a stable power supply during diagnosis.
Visually inspect BCM enclosure, mounting, and connector for water, corrosion, heat damage or loose mounting points. Repair any harness damage.
Check fuses/relay feeding BCM and measure supply and ignition-switched voltages at the BCM connector pins. Verify good ground to chassis at BCM ground terminal.
Scan vehicle network: look for U-codes, bus-off states, high error counters, or other modules losing communication. Isolate bus wiring if necessary.
If power/ground and bus wiring are good, attempt to clear the fault and operate affected systems while monitoring bus activity and BCM behavior.
If available, check BCM internal error/logging using dealer-level diagnostics or manufacturer software for memory/checksum errors or firmware status.
Attempt a software reflash/update or perform a controlled reset per OEM procedure. Some BCM faults are resolved by reprogramming.
If the BCM still fails diagnostic tests or shows internal hardware/memory errors, confirm with a known-good BCM or bench test (if possible) then replace the BCM and program/configure to vehicle.
After repair, verify all body functions, clear codes, and monitor for return of B0240 or related codes.

Likely causes

Failed internal regulator or voltage transient damage to BCM circuitry
Corrupted internal flash memory or checksum error
Intermittent ground or battery feed to BCM
Corroded connector pins or socket causing poor contact
Severe CAN bus fault (short to battery/ground) causing internal fault detection

Fault status

⚠️ Status

BCM internal fault detected — module self-test identified a hardware, memory or internal communications error. Module may report loss of communication or disable body functions.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours