B3470

Code

Generic B — Body

Body Control Module (BCM) Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 12 EN: 13 RU: 8

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Page language: EN

No communication with BCM on diagnostic scan tool (module not present)
Multiple body electrical functions inoperative or intermittent (locks, lights, wipers, windows)
Warning lamps or messages about communications/network failure
Erratic operation of accessories controlled by BCM
Other modules showing network errors or going into limp/limited mode

Record all stored codes from all modules with a capable scan tool; note any network-related codes
Verify battery voltage and charging system (minimum 12.2 V at rest for diagnostics)
Inspect fuses and power feeds for the BCM
Visually inspect BCM connectors and wiring for corrosion, damage, or loose pins
Check module ground(s) for security and low resistance to chassis
Confirm scan tool can see other network modules to verify bus is present

CAN bus idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V
CAN bus dominant: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V
Typical CAN termination: ~60 Ω between CAN_H and CAN_L (two 120 Ω resistors in parallel)
Common CAN bit rates: 500 kb/s, 250 kb/s, 125 kb/s (verify vehicle-specific rate)
LIN idle: LIN ≈ battery voltage via pull-up; dominant low near ground when driven
Expected: periodic BCM messages/IDs on the bus when channel monitored with a scanner or scope

Confirm the fault: connect a diagnostic tool, read and record codes from all modules and note any network status messages.
Check battery and fuses: verify battery state-of-charge and inspect/replace fuses supplying BCM power.
Visual inspection: open and inspect BCM connectors and wiring for corrosion, bent pins, or water ingress; repair as needed.
Verify grounds and power: measure voltage at BCM power terminals and check ground resistance to chassis (
Confirm network presence: verify other modules respond on the same bus. If only BCM missing, focus on its local wiring and connector.
Measure bus signals: with ignition ON, measure CAN_H and CAN_L voltages at the BCM connector; compare to expected signal_params.
Check bus termination and continuity: measure resistance between CAN_H and CAN_L (around 60 Ω) and perform continuity checks to other nodes.
Isolate faulty node: if bus is noisy or shorted, disconnect suspected modules one at a time (starting with BCM harness) to identify offending node.
Inspect for intermittent faults: perform wiggle test and road/test with scan tool to reproduce intermittent communication loss.
Reflash/replace: if wiring and power/ground are good and fault persists, verify BCM software/calibration and reprogram or replace BCM as per manufacturer procedures.
Verify repair: clear codes, exercise related systems, and confirm the B3470 does not return and network communications are stable.