B3730

Code

Generic B — Body

Body Control Module Internal Fault

Brand: Generic

Type: B — Body

Views: UK: 9 EN: 12 RU: 10

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Page language: EN

Causes

Internal BCM processor, memory (EEPROM/flash) or peripheral failure
Corrupted or incompatible BCM software/calibration
Intermittent or low supply voltage to the BCM (battery/ignition/starter-related)
Poor ground connection or corroded/loose BCM connector pins
Water ingress or physical damage to the BCM
Voltage spikes or reverse polarity events (jump-start, charging system fault)

Symptoms

One or more body systems inoperative or intermittent (lighting, locks, windows, wipers, HVAC blower)
Warning lamps or message center alerts related to body systems or module failure
No communication with BCM on diagnostic scan tool or erroneous module responses
Unexpected module reboots, chimes, or alarm/immobilizer faults
Failures that occur after battery disconnect, jump-start, or software update

What to check

Retrieve all stored codes and freeze-frame data from BCM and other modules using a capable scan tool
Attempt to clear the code and cycle ignition to see if code returns
Check battery voltage (resting and cranking) and charging system for stability
Inspect BCM connector, pins and wiring for corrosion, bent pins, water ingress, or damage
Verify good chassis and engine grounds associated with the BCM
Check fuses and fusible links for BCM power feeds

Signal parameters

Battery voltage at BCM connector (key off, key on, during cranking)
Ground continuity and voltage drop between BCM ground and chassis
CAN bus traffic and error frames (CAN_H/CAN_L voltages and waveform)
LIN bus activity if used by vehicle for body functions
BCM wake/sleep state and module awake percentage from scan tool
Internal self-test/failure flags, EEPROM checksum or software version reported by scan tool

Diagnostic algorithm

Read all DTCs and freeze-frame data from the BCM and related modules. Note any communication or power-related codes.
Attempt to clear B3730 and reproduce: cycle ignition and operate affected circuits to determine if fault is intermittent or permanent.
Verify battery and charging system health. Repair any low-voltage or charging faults before proceeding.
Visually inspect BCM connector and wiring for corrosion, bent pins, water intrusion, or rodent damage. Repair as needed.
Check power and ground at the BCM connector with a DMM. Verify voltage presence on all required supply pins with key on/off and during cranking.
Use a scan tool to monitor CAN/LIN bus messages while exercising body functions. Look for lost messages, high error rates, or a physically dead module.
If applicable, check BCM internal data (software/calibration version, EEPROM checksum) with OEM-level diagnostic software. If corruption is suspected, follow manufacturer's reprogramming or reflash procedure.
Perform wiggle tests on wiring harnesses while monitoring for code return to identify intermittent connector or wire faults.
If hardware fault is suspected after verifying power, grounds and communications, consider module repair or replacement. Only replace the BCM after confirming external causes are eliminated and follow OEM coding/pairing procedures (immobilizer/key programming may be required).
After repair or replacement, clear codes and verify all functions and communications over an extended test drive/operation period.