B2138 — Body Control Module Communication Fault (B2138)

Causes

• Intermittent or failed BCM (internal electronics)
• Open or shorted wiring on BCM power, ground or data lines (CAN/LAN)
• Corroded or loose BCM connector pins
• Blown fuse or lost power feed to BCM
• Poor or high resistance ground(s)
• Faulty termination or short on the vehicle data bus (CAN/LIN)

Symptoms

• Multiple body systems inoperative or intermittent (locks, lights, wipers, interior functions)
• Instrument cluster warnings or network communication warnings
• Central locking, keyless entry, or alarm malfunctions
• Erratic or no interior lighting, dome lights, or courtesy functions
• Some convenience features work intermittently or not at all
• Possible inability to perform remote diagnostics or reprogramming

What to check

• Scan vehicle with a capable diagnostic tool — read all stored and pending codes and note module(s) reporting communication errors
• Check battery voltage and charging system (should be ~12.4–12.8V at rest, >13.5V running)
• Inspect fuses and BCM power feeds for blown fuses or poor contacts
• Visually inspect BCM connectors for corrosion, bent pins, or water damage
• Backprobe BCM power, ignition feed, and ground pins for proper voltage and solid ground
• Measure CAN bus idle voltages at BCM connector (CANH and CANL) with key ON, engine OFF

Signal parameters

• Battery voltage at BCM supply pins: typically 11–14.5 V (engine running higher)
• Ground resistance at BCM: should be
• CAN idle voltages (key ON, engine OFF): CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V (recessive ~2.5 V)
• Dominant CAN states: CAN_H rises ~+1 V and CAN_L falls ~−1 V relative to recessive level
• Bus termination resistance (two 120 Ω resistors in parallel): ≈ 60 Ω across CAN_H to CAN_L
• Typical alive message frequency from BCM: varies by vehicle (often 1–10 Hz) — verify with scope or lab tool

Similar codes