B29B2

Code

Generic B — Body

Body Control Module — CAN Bus Communication Fault (Intermittent)

Brand: Generic

Type: B — Body

Views: UK: 11 EN: 13 RU: 9

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Page language: EN

Causes

Intermittent open/short in CAN_H or CAN_L wiring
Corroded or loose connector pins at BCM or other modules
Poor battery/ground connections affecting module operation
Failing CAN transceiver inside the BCM or another module on the same bus
Aftermarket device or harness tapping into the CAN bus causing noise or excessive load
Damaged termination resistor or incorrect termination network

Symptoms

Intermittent loss of BCM-controlled functions (lights, locks, wipers, etc.)
Other modules report communication errors or loss of data from BCM
Instrument cluster may freeze, show incorrect messages or illuminate multiple warning lamps
Random module resets or features working intermittently
DTCs for multiple modules appear or disappear depending on driving/use
CAN bus-related diagnostic trouble codes and transient codes stored

What to check

Use a diagnostic scanner to read DTC history and capture any related U- or B-codes and freeze-frame data
Visually inspect BCM and other module connectors for corrosion, bent pins, moisture, or pushed-out terminals
Inspect CAN wiring along routing for chafing, pinch points, heat damage, or evidence of repairs
Check battery voltage and main ground straps for corrosion, tightness and secure mounting
Disconnect suspicious aftermarket devices that tap into vehicle networks and re-test
Verify network topology: identify all modules on the same CAN bus and any gateway modules

Signal parameters

Idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each to chassis)
Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential present)
Differential voltage (dominant) ≈ 2.0 V
Termination resistance across CAN_H–CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel)
Common CAN data rates: 250 kb/s or 500 kb/s (verify vehicle-specific rate)
Bus load: should not be continuously saturated; check message frequency and error counters

Diagnostic algorithm

Scan and record all stored and pending DTCs, freeze-frame and event counters. Note times and conditions for intermittent events.
Check power and ground to BCM: verify battery voltage at BCM connectors and inspect ground strap(s). Repair any poor connections.
Visually inspect BCM and neighboring module connectors, harness sections and body grounds. Repair or reseal corroded connectors and damaged wiring.
With ignition on, monitor CAN traffic with a capable scan tool or CAN monitor. Confirm BCM messages appear at expected intervals and note missing or corrupted frames.
Measure CAN_H and CAN_L with a digital multimeter (key on, engine off). Expect approx. 2.5 V each; measure differential with oscilloscope to confirm recessive/dominant waveform and clean edges.
Measure resistance between CAN_H and CAN_L with power off; expect ~60 Ω. If out of range, inspect termination resistors and module presence.
Perform wiggle testing while monitoring the bus and watching for appearance/disappearance of errors to locate an intermittent connector or harness fault.
Disconnect non-essential modules or suspected aftermarket devices (one at a time) to isolate the fault. Re-test after each change.
If waveform shows noise or abnormal levels, capture oscilloscope traces during an event to provide to a specialist or for parts replacement justification.
If wiring and connectors check good, consider BCM or another module replacement only after confirming with scope/bench tests; reflash or update module software per manufacturer TSBs where available.
After repairs, clear codes, perform a drive cycle or exercise relevant functions to confirm the intermittent fault no longer occurs and re-scan.

Likely causes

Loose or corroded connector at BCM or gateway module
Chafed wiring rubbing to ground creating intermittent short to chassis or battery
Intermittent ground or battery connection causing module resets
Faulty CAN transceiver in BCM (intermittent failure)
Unterminated or incorrectly terminated network due to missing/failed resistors
Aftermarket alarm/telemetry device injecting noise or dominant bits

Fault status

⚠️ Status

Intermittent CAN bus communication fault detected by Body Control Module — transient loss or corruption of CAN messages between BCM and the vehicle network. Fault may clear when communication restores but will reappear while the root cause persists.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours