B1C14

Code

Generic B — Body

Body Control Module CAN Bus Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 10 EN: 18 RU: 14

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Page language: EN

Causes

Open or short in CAN high or CAN low wiring
Corroded, loose, or damaged BCM connector or other module connectors
Failed BCM or another networked control module
Improper or missing CAN network termination (faulty/missing 120Ω resistor)
Low or intermittent battery voltage or poor ground(s) affecting module operation
Intermittent wiring contact (pin pushed out, broken strand)

Symptoms

Multiple modules show communication errors or go into limp/fail-safe mode
Nonfunctional body functions controlled by BCM (lights, locks, wipers, etc.)
Intermittent or constant instrument cluster warnings about network faults
Inability to communicate with BCM using scan tool or limited parameter data
Erratic operation of features that rely on CAN messages

What to check

Retrieve freeze frame and full network DTC snapshot with a capable scan tool; note which networks (CAN High/Low, CAN FD) are affected
Check for additional U- or B- codes and the time stamp/conditions
Visually inspect BCM connector(s), harness immediately adjacent to BCM, and nearby ground points for corrosion, bent pins, or water damage
Check vehicle battery voltage (should be stable ~12–14.5 V) and main ground connections
Check for recently installed aftermarket modules or accessories on the CAN network and disconnect them for test
With ignition on, verify whether other control modules respond to the scan tool (to scope network reachability)

Signal parameters

CAN_H idle ~2.5 V (typical), CAN_L idle ~2.5 V; differential (CAN_H − CAN_L) ~0 V at recessive
Dominant state: CAN_H ≈3.5 V, CAN_L ≈1.5 V (approximate values; vary by vehicle)
Proper termination: two 120 Ω resistors in parallel ≈60 Ω across CAN_H to CAN_L (verify Ω with power off)
Normal bit rates commonly 250 kb/s or 500 kb/s (verify vehicle-specific rate)
Bus-off condition: module may report bus-off or high error counters and stop transmitting

Diagnostic algorithm

Confirm code and attempt to re-create conditions; record which modules are responding on the network with a scan tool
Check battery voltage and chassis/engine/BCM ground integrity; repair any low/poor grounds
Visually inspect BCM connector and harness for damage, corrosion or moisture; repair as required
With ignition ON (engine off), measure CAN_H and CAN_L voltages at BCM connector: compare to expected idle voltages and to a known-good module if available
With power off, measure resistance between CAN_H and CAN_L at two points to confirm termination ≈60 Ω; isolate wiring segments if resistance is incorrect
Use a lab scope or CAN bus analyzer to look for valid differential CAN frames, noise, repeated error frames or continuous dominant state; note whether frames originate from BCM or other nodes
If scope shows heavy faults, unplug suspected module(s) (starting with recently serviced/aftermarket devices) one at a time to see if bus returns to normal; always follow manufacturer safety and anti-theft procedures when disconnecting modules
Inspect and wiggle-test harness sections while monitoring the bus for intermittent faults; repair broken wires, chaffing or poor splice connections
If wiring and connectors are good but BCM still reports fault and bus is healthy, perform software reflash or replacement of BCM per manufacturer procedure
After repairs, clear DTCs and verify normal communication over a representative drive cycle or test sequence; confirm no recurrence

Likely causes

Poor or corroded BCM connector or ground
Short/open in CAN_H or CAN_L near BCM
Failed BCM or a nearby module putting the bus into bus-off state
Missing/failed termination resistor causing reflections or no bus

Fault status

⚠️ Status

BCM has detected invalid or absent CAN bus communication (timeouts, bus-off or signal fault) between the Body Control Module and the vehicle network. Communication is degraded or lost.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 3.0 hours

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