Code
B1115
HUMMER
B — Body
Body Control Module (BCM) Communication Fault
AI status
Completed
Completed
100%
Causes
- Open, short or high resistance in CAN/communication wiring or connectors
- Poor battery voltage or poor ground to BCM
- Blown fuse or faulty power/ignition feed to BCM
- Faulty BCM or other module pulling the bus down
- Corroded or water-damaged connector at BCM or junctions
- Aftermarket electrical accessories incorrectly installed
Symptoms
- Multiple body functions intermittent or inoperative (door locks, interior lights, wipers, windows)
- Warning lamps or messages related to communication faults
- Erratic operation of modules that rely on BCM messages
- Modules appear 'asleep' or do not respond to scan tool
- Codes for lost communication with other modules (U-codes) may be present
What to check
- Use a scan tool to read all stored/active DTCs and freeze frame; note time and ignition state
- Verify good battery voltage (12.4–12.9 V at rest, >13 V with engine running) and clean battery terminals
- Inspect BCM connectors and harness for corrosion, bent pins, water intrusion, or damage
- Check BCM power and ground circuits, and verify fuses/relays for BCM power feed
- Check for other communication-related U-codes that identify affected modules
- Measure CAN bus voltages with key on, engine off (see signal parameters) and check for proper idle levels and differential
Signal parameters
- Battery voltage: ~12.4–12.9 V resting, >13 V with engine running
- BCM power feed: near battery voltage with key on
- BCM ground:
- CAN bus idle voltages (node-level): CAN_H ~2.5 V, CAN_L ~2.5 V (approx.); differential idle ≈ 0 V - both sit near 2.5 V
- CAN bus dominant state: CAN_H ~3.5 V, CAN_L ~1.5 V when messages are transmitted (verify with scope)
- Bus bit-rate and waveform should be clean with no excessive ringing or stuck dominant bits
Diagnostic algorithm
- Record all DTCs and freeze frame data with a capable scan tool; note ignition state and recurring patterns.
- Verify battery condition and BCM supply/ground voltages; repair any low-voltage or poor-ground issues and recheck.
- Inspect BCM connector and harness visually for damage, corrosion, or water ingress; repair or reseal as needed.
- Check BCM power fuses and relays; replace if blown and evaluate cause of blown protection devices.
- Check for related U-codes that indicate which modules have lost communication to narrow the faulted network segment.
- Measure CAN_H and CAN_L at BCM with key ON, engine OFF. If voltages are out of expected ranges, isolate wiring for short/open.
- Use an oscilloscope to view CAN waveforms to identify collisions, stuck dominant bits, or intermittent noise; perform wiggle tests on harness.
- Disconnect non-essential modules or suspect nodes (one at a time) to see if the network recovers; this can identify a shorting node.
- If wiring and external modules check good and bus signals are correct, suspect BCM internal transceiver or internal failure—verify with manufacturer service data.
- If BCM replacement is required, follow OEM procedures for replacement, programming and configuration; clear codes and confirm repair by road test and re-scan.
Likely causes
- Damaged CAN High or CAN Low wiring near BCM or harness chafe
- Loose or corroded BCM ground or battery terminal
- Blown BCM power fuse or fusible link
- Failed BCM internal transceiver
- Intermittent short to battery or ground from an accessory
Fault status
Status
BCM Communication Fault — loss or interruption of network messages to/from the Body Control Module. Further electrical and network diagnostics required.
Repair difficulty: Medium
Diagnostic time: 1.5-4.0 hours
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Repair manuals
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138
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