B0500

Code

Generic B — Body

Body Control Module (BCM) Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 15 EN: 29 RU: 15

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Page language: EN

Causes

Low battery voltage or poor battery connection
Faulty BCM (internal failure)
Open/shorted wiring or poor connector at BCM
Damaged or missing CAN/LIN bus termination or wiring
Grounding problems at BCM or other network modules
Corroded or loose fuse/relay supplying BCM power

Symptoms

Inability to communicate with BCM via scan tool
Multiple body electrical failures (lights, locks, windows)
No remote keyless entry or alarm operation
Intermittent instrument cluster messages or warnings
Possible no-start or crank-related interlocks if BCM controls immobilizer
Battery drain or parasitic draw in some cases

What to check

Verify battery voltage is within specification (start/idle and cranking)
Connect a capable scan tool and attempt to communicate with BCM and other modules
Check for related U-codes (CAN network) and freeze-frame data
Visually inspect BCM connectors, wiring harness, and nearby components for damage or corrosion
Check BCM power and ground circuits for proper voltage and low resistance to chassis
Measure CAN_H and CAN_L idle voltages and check termination resistor (~60 ohms between lines)

Signal parameters

CAN idle: CAN_H ≈ 2.5V and CAN_L ≈ 2.5V (recessive); dominant: CAN_H ≈ 3.5V / CAN_L ≈ 1.5V
CAN differential during messages: nominally ~2.0V
Termination resistance: approx. 60 ohms between CAN_H and CAN_L (two 120Ω in parallel)
LIN bus wake/sleep voltage levels per vehicle specification (typically 12V or battery reference for wake signals)
Module supply voltage at BCM pins (battery voltage when ignition on)
Network error/frame counters and message frequency from scan tool

Diagnostic algorithm

Record DTCs and freeze-frame data from all modules; note any U-series network codes.
Verify battery state of charge and clean battery terminals; retest communications.
Try communicating with BCM using a known-good scan tool/adapter to rule out tool compatibility.
Inspect BCM connectors and wiring for corrosion, bent pins, or water intrusion; repair as needed.
With ignition on, measure power and ground at BCM power pins; confirm correct voltages and low ground resistance.
Backprobe CAN_H and CAN_L at the BCM and another module; verify idle voltages and differential and check for messages with an oscilloscope or lab scope if available.
If bus voltages or termination are wrong, isolate segments (disconnect modules or split harness) to find short/open or high resistance splice.
Remove or disable aftermarket devices and retest; repair any vehicle wiring faults found.
If wiring and network are good and software versions mismatch, check for required BCM reprogramming or configuration and perform per OEM procedures.
If all network wiring, power/ground, and software are verified and the BCM still does not communicate, consider BCM replacement following proper immobilizer and module programming steps.

Likely causes

Loose or corroded power/ground at the BCM
Broken CAN or LIN bus wire near BCM or splice
Missing or shorted termination resistor on CAN bus
Intermittent connector pins at BCM
Failed BCM due to internal electronics or water ingress

Fault status

⚠️ Status

Body Control Module communication fault detected — BCM not communicating reliably on vehicle network. Check power, ground, wiring, and network integrity before replacing module.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours