B1C36

Code

Generic B — Body

Body Control Module CAN Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 16 EN: 21 RU: 14

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Page language: EN

Instrument cluster or other modules show communication-related warnings
Door locks, lighting, windows, remote functions do not respond or are intermittent
Multiple modules throw related communication codes
Certain functions work intermittently or stop after vehicle sits
Unrelated systems disabled due to network loss (e.g., immobilizer, theft system)
No CAN messages from BCM seen on a scan tool or low message frequency

Retrieve all communication and BCM-related DTCs from BCM and other modules with a capable scanner
Read freeze frame and history to determine when faults occur (key-on, load, driving, after wash)
Visual inspection of BCM area, connectors, harness for corrosion, damage, water
Check battery voltage (key on and cranking) and fuses supplying BCM and CAN transceiver
Inspect grounds for tightness and corrosion at BCM and chassis ground points
Use a scan tool to view CAN bus message list and module presence/IDs

Recessive idle: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each ~2.5 V)
Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Termination resistance: ≈ 60 Ω measured between CAN_H and CAN_L (two 120 Ω terminators in parallel)
Typical bit rates: 250 kb/s or 500 kb/s depending on vehicle (match expected network speed)
Expected messages: BCM transmit ID(s) and regular message frequency — scan tool should show steady periodic frames from BCM

Confirm code and record freeze frame and related DTCs from all modules
Check battery voltage and secure/fuse power to BCM; restore power if low or fuse blown
Perform a visual inspection of BCM connector and wiring; unplug and inspect pins for corrosion or damage
Measure termination resistance between CAN_H and CAN_L with ignition off (≈60 Ω). If abnormal, isolate sections to find missing/bad terminator
Using an appropriate scan tool, confirm whether BCM appears on the CAN network and note missing message IDs and frequencies
With ignition on, backprobe CAN_H and CAN_L at BCM and observe voltages with a digital multimeter; then use an oscilloscope to verify clean CAN waveform and correct dominant/recessive levels
Wiggle harnesses and connectors while monitoring network traffic and DTCs to find intermittent wiring faults
If a short is suspected, isolate by disconnecting modules segment-by-segment (start near BCM) until bus returns to normal; repair shorted wiring or replace damaged connectors
Check and repair any faulty grounds or power feeds to BCM; re-check communication after repairs
If wiring and power/grounds check OK and the network is correctly terminated but fault persists, check for software updates or reprogramming notes from OEM; only replace BCM after confirming module failure with evidence (no messages, failed transceiver, or diagnostic confirmation)
Clear codes and retest the vehicle through typical operating conditions to verify repair

Loose or corroded BCM connector pins
Short to battery or ground on CAN_H or CAN_L near the BCM
Failed BCM after water intrusion or impact
Blown fuse supplying BCM logic or transceiver
Faulty gateway or another module holding the bus dominant
Missing/failed 120 Ω terminator (resulting in ~120 Ω instead of ~60 Ω across bus)