B1C68

Code

Generic B — Body

Body Control Module Network Communication Intermittent (Bus C)

Brand: Generic

Type: B — Body

Views: UK: 9 EN: 10 RU: 9

AI status

Completed

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Page language: EN

Causes

Damaged or corroded wiring or connectors on Bus C
Poor or intermittent ground or battery supply to BCM or other nodes on Bus C
Loose, bent, or poorly seated module connectors (BCM or other network nodes)
Failing BCM or other control module on Bus C
Faulty or missing bus termination resistor(s)
Electrical interference (EMI) or short to power/ground on the bus

Symptoms

Intermittent or sporadic electrical accessory operation (lighting, locks, windows, etc.)
One or more control modules intermittently not responding to scan tool
Multiple network communication DTCs stored (intermittent)
Warning lamps that come on and off (e.g., BCM-related warnings)
Vehicle functions that work intermittently or only after ignition cycles
No permanent economic code but repeated intermittent communication faults

What to check

Read all stored and pending codes and freeze-frame data from all modules
Check for related U-codes (lost communication) and time stamps to correlate events
Inspect BCM and other Bus C module connectors for corrosion, bent pins, water, or damage
Measure battery voltage and check grounds at BCM and nearby modules
Perform wiggle test on harness and connectors while monitoring bus with scan tool/oscilloscope
Check bus termination resistance (typical combined ≈ 60 Ω for CAN); inspect for removal or damage

Signal parameters

For CAN: idle CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V; dominant state differential ≈ ±2 V (verify against OEM spec)
Bus differential voltage normally toggles between dominant and recessive; excessive noise, spikes, or stuck levels indicate faults
Termination: combined end-to-end resistance usually around 60 Ω for two 120 Ω terminators (verify vehicle-specific value)
Error counters and error frames will increase on the bus during intermittent faults (viewable with diagnostics tool)
Data rates vary by application (e.g., 125 kbps–1 Mbps for CAN); confirm Bus C data rate in service documentation

Diagnostic algorithm

Capture all current, pending, and historical DTCs from all modules. Note the ignition/run conditions and freeze-frame data.
Check battery voltage and charging system; low voltage or brownout can cause intermittent communications. Repair as needed.
Visually inspect BCM and all Bus C module connectors, harness routing, and splice points for corrosion, damage, water ingress, or poor seating. Repair or re-seat connectors.
Backprobe BCM power and ground pins to verify stable supply and good chassis/ battery ground while cycling ignition and reproducing fault conditions.
With a capable scan tool, monitor Bus C messages and module presence while performing a wiggle test on harnesses and connectors to try to reproduce the intermittent fault.
If available, use an oscilloscope or CAN/LIN analyzer to observe physical layer signals on Bus C for noise, missing frames, dominant stuck states, or excessive error frames. Record waveform during failure.
Measure bus termination resistance with power off; confirm termination values per service manual. Repair/replace termination resistors or wiring as required.
Isolate nodes: disconnect suspected modules one at a time (with key off per procedures) and re-test the bus to identify a node causing errors. Replace or repair faulty node if identified.
Check for and install any BCM or related module software updates or reflash firmware if the OEM procedure addresses intermittent communication issues.
After repairs, clear codes and road-test under conditions that previously produced the fault. Re-scan to confirm B1C68 does not return.
If intermittent fault persists and wiring & connectors are good, consider bench-testing or replacing the BCM per OEM diagnostic guidelines.

Likely causes

Intermittent connector contact (loose pin, corrosion) at BCM or another module
Open, short, or high-resistance connection in Bus C wiring
Intermittent supply/ground to BCM or a node causing the node to drop off the bus
Failed module periodically driving bus incorrectly or introducing noise
Missing or degraded bus termination causing reflections/intermittent errors

Fault status

⚠️ Status

Intermittent communication fault detected on Body Control Module network Bus C — module(s) occasionally fail to communicate or bus messages are corrupted.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours