B29B9

Code

Generic B — Body

Body Control Module CAN Communication Timeout

Brand: Generic

Type: B — Body

Views: UK: 4 EN: 11 RU: 5

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Page language: EN

Causes

Open or intermittent wiring on CAN‑H/CAN‑L to the BCM
Poor ground or battery power to the BCM
Faulty CAN transceiver inside the BCM
Missing or failed module elsewhere on the CAN bus
Improper or failed termination resistor(s) on the CAN network
Corroded/loose connectors at BCM or other modules

Symptoms

BCM‑related features nonfunctional (lights, door locks, wipers, keyless functions)
Intermittent or permanent loss of communication with BCM on scan tool
Other modules showing communication errors or limp mode
Related interior lamps or warnings illuminated
No periodic BCM CAN messages visible on network trace

What to check

Connect a calibrated scan tool and read all stored and pending codes from BCM and other modules
Confirm vehicle battery voltage and BCM supply/ignition feed (key ON)
Check for presence of BCM on network (tool reports module present) and note any U‑codes on other modules
Inspect BCM and nearby harness connectors for corrosion, bent pins, water intrusion, or damage
Visually inspect CAN wiring for chafing, pinched areas, or recent service work
Measure CAN bus termination resistance between CAN‑H and CAN‑L (typical ~60 ohms for two 120Ω terminators)

Signal parameters

CAN physical idle voltages (typical): CAN‑H ≈ 2.5 V (recessive) to ≈ 3.5 V (dominant); CAN‑L ≈ 2.5 V (recessive) to ≈ 1.5 V (dominant)
Differential voltage: recessive ≈ 0 V, dominant up to ~2 V
Common CAN bus data rates: 125 kbps, 250 kbps, 500 kbps, or 1 Mbps depending on network — verify vehicle‑specific rate
Expected BCM message cadence: periodic transmit/receive intervals typically tens to hundreds of ms (vehicle specific). Timeout occurs when expected message(s) are not received within configured window

Diagnostic algorithm

Record freeze frame, history and all related codes from BCM and other modules with a scan tool.
Verify battery voltage and BCM ignition/ignition‑feed power and grounds; repair any low/poor connections.
Inspect BCM connectors and harness for damage, corrosion or water intrusion; repair connector issues before further testing.
With key ON, check for CAN presence via scan tool: is BCM present? Are other modules showing CAN messages? Note any missing nodes.
Measure CAN‑H and CAN‑L voltages at the BCM connector with a multimeter (key ON). Compare to expected values; check termination resistance between CAN‑H and CAN‑L (~60Ω for most networks).
If voltages and termination are within range but communication missing or intermittent, capture CAN traffic with a diagnostic tool or oscilloscope. Look for missing message IDs, extended delays, dominant/short pulses, reflections, or excessive noise.
Isolate the fault by disconnecting nonessential modules or segments one at a time (while observing network behavior) to find a module or harness section that restores normal traffic when removed.
If an aftermarket device is present, disconnect it and retest.
If wiring and other modules check good, consider reflashing/updating BCM software or reinitializing network settings per manufacturer procedures.
If reflash/configuration fails and fault persists and testing points to internal transceiver or BCM failure, replace BCM or its transceiver module and reconfigure coding/calibrations as required.
After repairs, clear DTCs and verify normal CAN traffic and BCM functions over a drive/operation cycle.