B2400

Code

Generic B — Body

Body Control Module (BCM) Power Supply Fault

Brand: Generic

Type: B — Body

Views: UK: 31 EN: 77 RU: 45

AI status

Completed

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Page language: EN

Causes

Low or discharged battery
Blown fuse or fusible link feeding the BCM
Faulty ignition/accessory relay or wiring
Corroded/damaged BCM power or ground connections
Short/open in wiring harness to BCM power pin
Intermittent supply due to connector contamination or water intrusion

Symptoms

Illumination or flicker of interior/exterior lights
Intermittent or total loss of body functions (door locks, wipers, windows, interior lights)
Multiple body module communication errors on scan tool
Instrument cluster warnings or inoperative displays
Accessories operate only intermittently or not at all
Vehicle may fail to unlock/lock or show odd behavior after key on

What to check

Check battery state-of-charge and terminal condition (clean/tight).
Inspect BCM area and connectors for corrosion, water intrusion, bent pins, or physical damage.
Check all fuses and fusible links related to body/control modules and accessory circuits.
Verify ignition/key switch and accessory relays that supply BCM power.
Scan vehicle for additional U- or B-codes indicating communication faults.
Measure voltage at BCM power feed pin with key OFF and key ON; measure ground continuity between BCM ground and battery negative.

Signal parameters

Battery supply to BCM: ~11–14.6 V (engine off/charging vary) at battery terminals and at BCM power pin with key ON.
Ground: near 0 V; low resistance (
Ignition-switched feed present when key ON; should be near battery voltage when active.
CAN bus recessive level ~2.5 V on both CAN_H and CAN_L (verify against vehicle spec).
Key wake/sleep signals meet manufacturer timing and voltage specs (refer to service manual).

Diagnostic algorithm

Record freeze frame and all related codes; note operating conditions when fault occurred.
Verify battery voltage and health. Charge or replace battery if low and retest.
Visually inspect BCM, mounting, connector sealing and wiring for damage/corrosion/water intrusion. Repair any found issues.
Check fuses/fusible links and relays feeding the BCM; replace any blown components. Verify relay operation and coil feed/ground.
With a DVOM, measure voltage at the BCM power pin(s) with key OFF and key ON; compare to battery terminal voltage. Look for voltage drops.
Measure resistance/continuity from BCM ground to battery negative. Clean and tighten ground connections as required.
Backprobe power and ground while operating affected circuits or performing a wiggle test to detect intermittent faults.
Verify communication bus presence (CAN/LIN) and proper levels with an oscilloscope or lab scope if available.
If wiring and supplies are confirmed good and within specification, consider BCM internal fault. Verify software/calibration and update if available before replacing module.
If BCM replacement is required, follow manufacturer procedures for programming/encoding and protect anti-theft/immobilizer systems. Clear codes and retest road/use cycle to confirm repair.

Likely causes

Blown BCM fuse or fusible link
Loose or high-resistance ground at BCM or chassis
Ignition-switched feed open or intermittent (relay or wiring)
Corroded or water-damaged BCM connector pins
Battery voltage sag under load or poor battery connections

Fault status

⚠️ Status

BCM power supply outside expected range — low/absent/intermittent supply, fuse/relay/wiring/ground issue or internal BCM fault. Verify supply and grounds before replacing module.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours