B1B39

Code

Generic B — Body

Body Control Module: CAN Bus Communication Error (Node 39)

Brand: Generic

Type: B — Body

Views: UK: 16 EN: 13 RU: 12

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or shorted CAN_H or CAN_L wiring to node 39
Poor power or ground to the BCM or the affected node
Disconnected, corroded or damaged connector/pins at BCM or node 39
Missing or incorrect termination resistors (broken/removed 120 Ω terminators)
Short to battery (+B) or chassis ground on the CAN pair
Faulty BCM or the other node (node 39) electronics

Symptoms

Service messages or warning lights related to body systems
Loss or intermittent operation of devices controlled by node 39 (locks, lights, windows, etc.)
Unable to communicate with node 39 using a scan tool
Multiple communication-related DTCs (U-codes) present
Intermittent functionality of unrelated modules when the bus is disturbed

What to check

Read and record all stored DTCs and freeze-frame data with a capable OEM-level scan tool; note related U- and B-codes
Check battery voltage (should be 12.4–14.6 V with engine running) and charge state before testing
Visually inspect BCM and node 39 connectors for corrosion, bent pins, water ingress, or loose terminals
Check fuses and relays supplying BCM and node 39 power circuits
Wiggle test wiring harness around BCM, gateway, and node 39 while watching live CAN status on scan tool
Measure CAN termination resistance between CAN_H and CAN_L (expect ~60 Ω across the bus with key on, two 120 Ω terminators in parallel)

Signal parameters

Idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V, differential ≈ 0 V
Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V, differential ≈ 2.0 V
Typical termination resistance across CAN_H–CAN_L for a healthy network ≈ 60 Ω (two 120 Ω terminators in parallel)
Common CAN bit rates: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific rate before advanced tests)
No DC short to battery or ground on CAN wires (single-wire shorts will shift idle voltages)

Diagnostic algorithm

Use an OEM-capable scan tool to capture all DTCs and live CAN bus status; note whether the fault is present now or intermittent.
Verify vehicle battery state and fuses/relays for BCM and node 39 power/ignition circuits.
Visually inspect BCM and node 39 connectors and harnesses for damage, corrosion, water intrusion, or poor pin fit; repair any damage.
Perform basic electrical checks: verify proper power and ground at BCM and node 39 (voltage and continuity).
With key ON, measure termination resistance between CAN_H and CAN_L at multiple points; confirm ≈60 Ω. If open or very high, locate missing terminator.
Measure CAN_H and CAN_L voltages at BCM and node 39 with meter; compare to expected idle/dominant levels. Significant offset suggests short to Vb or ground or missing termination.
If voltages look normal, use an oscilloscope or CAN analyzer to inspect bus traffic and waveform integrity while exercising affected systems. Look for noise, missing frames, or a node flooding or pulling bus dominant.
Isolate the fault by disconnecting suspected nodes one at a time (with ignition per service procedure) to see if communication is restored; this can identify a faulty node that drags the bus down.
If a single module (node 39) is confirmed faulty by isolation and wiring/power/termination are good, reprogram/flash the module per OEM procedure, or replace if reflash does not correct the fault.
After repairs, clear codes, perform communication tests and a functional verification, and road-test to confirm fault does not return.

Likely causes

Damaged wiring or connector between BCM and node 39
Lost power/ground to the BCM or node 39
Failed node 39 module
Missing/incorrect CAN termination

Fault status

⚠️ Status

The BCM has logged that CAN messages to/from node 39 are missing, corrupted, or outside expected timing/levels. The condition may be intermittent or permanent and can result from wiring/connectors, termination, power/ground problems, or a failed module.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours