B2950

Code

Generic B — Body

Body Control Module Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 16 EN: 28 RU: 15

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Page language: EN

Causes

Loss of power or ground to the BCM (blown fuse, poor connector, corroded terminal)
Damaged or shorted wiring on the BCM harness
Open or short on the vehicle communication bus (CAN, LIN, or proprietary bus)
Failed BCM internal electronics
Incorrect or outdated BCM software/calibration
Faulty gateway or another module preventing bus traffic

Symptoms

Multiple body functions inoperative (lighting, locks, windows, wipers)
Intermittent or permanent warning lights on dash
Other modules report comms-related DTCs (U-codes)
No BCM responses when queried with a scan tool
Features work after battery disconnect/reset then fail again

What to check

Read all stored DTCs and freeze frame data from all modules; note related U- and B-codes
Confirm battery voltage is stable (12.4–12.9 V at rest; >13.5 V with engine running)
Inspect BCM fuses and power/ignition feeds for continuity and correct voltage
Visually inspect BCM connector(s) for corrosion, bent pins, water intrusion, or damage
Check main ground(s) for clean, tight connections and low resistance to chassis
Scan the vehicle bus for traffic; verify BCM is present and transmitting/receiving messages

Signal parameters

Battery/resting voltage: ~12.4–12.9 V; running: >13.5 V
CAN bus idle voltages (typical recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V
CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Termination resistance: ~60 Ω measured between CAN_H and CAN_L at rest (two 120 Ω in parallel)
Wake/standby supply: correct ignition/sleep wake voltages per vehicle spec
Module supply and ground resistance: expected low ohms to battery and chassis

Diagnostic algorithm

Verify battery state and reconnect if necessary; record battery/resting voltage.
Use a scan tool to read all DTCs and module presence. Note any U-codes or multiple module failures.
Check BCM power and ground circuits: verify voltages at BCM connector pins with key ON and engine running per wiring diagram.
Inspect BCM connector for corrosion, bent pins, or water intrusion; repair or replace connector as required.
Verify fuses and fusible links feeding the BCM; replace any blown fuses and retest.
With ignition ON, measure CAN_H and CAN_L voltages at BCM connector and measure termination resistance across H and L. Compare to expected values.
If bus measurements are abnormal, isolate segments: disconnect BCM and re-measure bus to locate short/open; inspect harness for damage and shorts to battery/ground.
Perform wiggle/stress tests on wiring while monitoring bus traffic and DTC return to identify intermittent harness faults.
Check for competing modules/gateways: verify other modules are responding and not holding bus dominant. Disconnect suspected aftermarket modules.
If wiring, power and grounds check good and software is older/out-of-date, check for available BCM software updates or reprogramming procedures and perform per OEM instructions.
If all wiring, power, communications and software checks pass and fault persists, consider BCM replacement. Program/configure replacement BCM per manufacturer procedure.
After any repair or reprogramming clear codes and confirm fault does not return under normal conditions and during road test.