B2D35

Code

Generic B — Body

Body Control Module CAN Bus Communication Error

Brand: Generic

Type: B — Body

Views: UK: 9 EN: 5 RU: 7

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Page language: EN

Causes

Open, short, or high resistance in CANH or CANL wiring or connector(s)
Poor BCM supply voltage or ground connection
Failed or intermittent BCM (module hardware fault)
Missing or incorrect bus termination (open or damaged resistor)
Another module on the same CAN bus stuck dominant or driving the bus incorrectly
Corroded or loose connectors or pin damage at BCM or gateway

Symptoms

Multiple modules show communication faults or fail to respond to a scan tool
Instrument cluster warnings, message center notifications, or lamp illumination
Central locking, windows, lighting, or other body functions operate intermittently or not at all
No communication with BCM or gateway when attempting to read with a scanner
Erratic or lost data shown by other modules that rely on BCM messages

What to check

Scan for all current and stored DTCs across all networks; record freeze-frame and occurrence data
Verify battery voltage and charging system; check BCM supply and ground circuits (voltage with key on and engine off)
Visually inspect BCM connectors and CAN wiring for corrosion, pin damage, chafing, or repairs
Measure resistance across CANH and CANL with power off; expected ≈ 60 ohms (two 120 Ω terminators in parallel) on that bus
Backprobe CANH and CANL with key on (engine off) to confirm idle voltages and common-mode voltage
Use an oscilloscope to observe CAN differential waveform for noise, dominant timeouts, or bus errors

Signal parameters

Recessive (idle) voltage: CANH ≈ 2.5 V, CANL ≈ 2.5 V (common-mode ≈ 2.5 V)
Dominant state voltages: CANH typically rises toward ≈ 3.5 V, CANL falls toward ≈ 1.5 V (differential ≈ 2.0 V)
Termination: nominal total bus resistance ≈ 60 Ω (two 120 Ω terminators in parallel)
Common CAN bit rates: 125 kbps, 250 kbps, 500 kbps, 1 Mbps — verify vehicle-specific rate
Acceptable idle common-mode voltage range commonly ±0.5 V around 2.5 V (check OEM spec)

Diagnostic algorithm

Retrieve and document all DTCs from all networks and note time stamps/freeze data. Clear codes and attempt to re-create the fault to confirm current status.
Verify battery voltage and measure BCM supply (VBatt) and ground integrity. Repair any low voltage or high-resistance ground conditions before further testing.
Visually inspect the BCM connector(s), harness routing, and any splice points for corrosion, bent pins, or evidence of water intrusion; repair as needed.
With ignition ON (engine OFF), measure CANH and CANL idle voltages at the BCM harness. Compare to signal parameter ranges. Power off vehicle and measure resistance between CANH and CANL — expect ~60 Ω.
Use an oscilloscope to observe the CAN differential waveform while exercising the network. Look for missing dominant edges, noise, reflections, repeated error frames, or a bus stuck dominant.
If bus is shorted or stuck, isolate by disconnecting modules (one at a time) or branches until the fault clears; inspect that disconnected module/harness for internal faults.
Inspect and verify termination resistors and any CAN repeaters/gateways. Replace open or out-of-spec termination components.
Remove aftermarket devices or accessories tied into the CAN and retest. Repair or isolate any improper taps.
If wiring, grounds, and other modules test good, consider BCM replacement or repair. Verify and perform OEM reprogramming/configuration after replacement.
After repairs, clear DTCs, verify all modules communicate, and perform a system test/road test to ensure the fault does not return. Document all findings.

Likely causes

Damaged wiring or connector corrosion at the BCM or along the CAN trunk
Loss of BCM power or ground causing the BCM to drop off the bus
Failed or weak termination resistor(s) (improper bus impedance)
Another control module driving CANH/CANL and pulling the bus out of spec
Intermittent BCM internal fault (requires module bench testing or replacement)

Fault status

⚠️ Status

BCM detected CAN bus communication fault — messages to/from the body network are missing or corrupted. Communication may be intermittent or permanently lost.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-4.0 hours