B29D1

Code

Generic B — Body

Body Control Module: CAN Bus Communication Error with Gateway

Brand: Generic

Type: B — Body

Views: UK: 11 EN: 14 RU: 12

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Page language: EN

Causes

Open, short or high resistance in CAN High / CAN Low wiring between BCM and Gateway
Missing, incorrect, or damaged termination resistor(s)
Faulty CAN transceiver in BCM or Gateway (internal module hardware failure)
Loss of power or poor ground to BCM or Gateway
Corroded or poorly seated connector(s) at BCM, Gateway, or inline splices
Excessive electrical noise or high bus load (aftermarket devices, sensors)

Symptoms

Loss or intermittent loss of body network functions (locks, lights, wipers, infotainment messages)
Multiple modules show communication-related DTCs (U-codes) or are unresponsive to scan tool
Instrument cluster or message center shows network warnings
Remote key or remote start not working
Modules enter limp or reduced-function mode; erratic body module behavior

What to check

Read and record all current and pending DTCs from BCM, Gateway and related modules; note freeze frame data
Check battery voltage and charging system; restore to nominal (12.4–12.8 V at rest) before tests
Visually inspect connectors, pins and harnesses at BCM, Gateway and along CAN route (look for corrosion, bent pins, water, damage)
Confirm no recent aftermarket installations splicing into CAN or power/gnd circuits
Check for related U-codes (e.g., U0100, U0073) that indicate wider network problems
Measure termination resistance between CAN High and CAN Low with ignition OFF (should be ~60 ohms total)

Signal parameters

CAN recessive state: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each to chassis)
CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (approx. ±1.0–1.5 V differential)
Differential voltage (CAN_H - CAN_L) ≈ 2.0 V when dominant, ≈ 0 V when recessive
Typical bit rates: 500 kbps (high-speed CAN) or 250 kbps/125 kbps depending on vehicle network
Bus termination: total ≈ 60 ohms between CAN_H and CAN_L with ignition OFF
Expected error-frame count: near 0 under normal conditions; observe for repeated error frames, retransmits, or bus-off events

Diagnostic algorithm

Retrieve and document all DTCs from BCM, Gateway and other network modules. Note freeze frame and occurrence count.
Verify battery voltage and main power/ground to BCM and Gateway; repair if out of range or intermittent.
Perform a visual inspection of connectors and harness along the CAN route (doors, hinges, junctions). Repair any damage or corrosion.
With ignition OFF, measure termination resistance between CAN_H and CAN_L at BCM/Gateway harness — expect ≈60 ohms total. If out of range, trace/remove extra termination or find open/short.
Power the vehicle and use an oscilloscope or CAN analyzer to monitor CAN_H/CAN_L at the BCM and Gateway. Look for clean recessive/dominant waveforms, proper amplitude, expected IDs, and absence of repeated error frames or bus-off conditions.
If noise, missing messages, or bus-off is observed, isolate segments by disconnecting non-essential nodes or harness branches (one at a time) to find the offending module or shorted branch.
Wiggle test connectors and harness while monitoring CAN traffic to reproduce an intermittent fault; repair wiring or connector as needed.
If wiring and termination verify OK, swap or bench-test suspected modules (BCM or Gateway) if a known-good unit is available or check for internal CAN transceiver fault codes per manufacturer procedures.
Check for software/firmware updates or calibration changes for BCM and Gateway; reflash or program per service instructions if recommended.
After repairs, clear codes, monitor for reoccurrence, and road test while scanning to ensure the fault is resolved and no other network errors return.

Likely causes

Open/short in CAN High or CAN Low between BCM and Gateway
Faulty CAN transceiver in BCM or Gateway
Missing or out-of-spec termination resistor (not ≈60 ohm total)
Power or ground issue to BCM or Gateway
Corroded/loose connector at either module

Fault status

⚠️ Status

Body Control Module detected a CAN bus communication error with the Gateway — messages missing, corrupted, or bus-off condition between BCM and Gateway.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours