B3622

Code

Generic B — Body

Body Control Module CAN Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 17 EN: 20 RU: 18

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Page language: EN

Causes

Open or shorted CAN_H or CAN_L wiring
Poor connector or pin contact (corrosion, bent pins)
Missing or damaged CAN termination resistor(s)
Low or unstable battery/charging system voltage
Faulty Body Control Module or another module on the same CAN segment
Software/firmware mismatch, corrupt calibration or missing gateway messages

Symptoms

DTC B3622 stored in BCM and possibly other U-codes appearing
Loss of functions controlled by BCM (lighting, locks, windows)
Intermittent or permanent loss of communication with some modules on scan tool
Multiple modules reporting invalid or missing data
Unusual CAN bus behavior (modules entering limp/inactive mode)
Vehicle may not start if immobilizer or gateway messages are lost

What to check

Verify battery voltage ≥12.4 V and charging system operation with engine running
Use a scan tool to read BCM and other network modules for additional U-/B-codes and active faults
Visual inspection of BCM connectors, nearby harness, and shielded CAN cable for damage or corrosion
Check fuses and relay supplies to BCM and related networks
Measure resistance between CAN_H and CAN_L with ignition off — expected ≈60 Ω (two 120 Ω terminators in parallel)
Backprobe or use oscilloscope to view CAN_H and CAN_L waveforms during cranking/operation

Signal parameters

CAN bus nominal bit rates commonly 125 kb/s, 250 kb/s, 500 kb/s or 1 Mb/s (verify vehicle spec)
Recessive idle voltages: CAN_H ≈2.5 V, CAN_L ≈2.5 V (each)
Dominant state voltages: CAN_H ≈3.5 V, CAN_L ≈1.5 V (differential ≈2.0 V)
Expected DC resistance between CAN_H and CAN_L with ignition off ≈60 Ω (both terminators present)
Short-to-ground or short-to-battery will show significant deviation from nominal voltages
Message rate and IDs vary by vehicle; missing periodic messages to/from BCM are diagnostic indicators

Diagnostic algorithm

Connect a capable diagnostic scan tool and record freeze frame and occurrence history; note any additional U- or B-codes
Verify vehicle battery and charging voltages; charge battery if low and retest
Visually inspect BCM and harness for damage, moisture, corrosion or loose connectors; reseat connectors and check pin condition
Check BCM power and ground circuits for proper voltage and low resistance to battery negative
With ignition off, measure resistance between CAN_H and CAN_L at BCM connector — expect ≈60 Ω. If open or much higher, locate broken terminator or open line
With ignition on, backprobe CAN_H and CAN_L at BCM and view with oscilloscope or high-speed data logger. Confirm valid CAN waveforms, proper differential amplitude, and lack of constant dominant state
If bus stuck dominant, isolate sections by unplugging modules one at a time to find the short or faulty node (do not unplug airbags or critical safety modules unless safe procedures followed)
Inspect and test suspect connectors/wiring found during isolation; repair broken wires, corroded pins, and replace damaged connectors
If wiring and termination are correct and the bus looks normal but BCM still reports faults, check for software updates or programming mismatch; reflash or update module software per manufacturer procedure
As final step, replace BCM only if bench or in-vehicle testing confirms BCM transceiver or controller failure. Reprogram new module as required
Clear codes and road-test to confirm repair; monitor for reappearance and re-check network messages

Likely causes

Wiring short to battery or ground on CAN pair
Broken wire or pin at a connector near the BCM
Failed BCM transceiver or internal CAN controller
Missing 120 Ω termination at one or both ends (should measure ~60 Ω across CAN_H/CAN_L)
Low battery voltage or poor ground at BCM causing transceiver failure
Another module flooding or holding the bus dominant