Code
B0748
HUMMER
B — Body
Body Control Module network communication lost
AI status
Completed
Completed
100%
Causes
- Lost or intermittent power to BCM (fuse, relay, wiring)
- Poor or missing ground at BCM
- Open, shorted or corroded CAN/GMLAN wiring or connectors
- Failed BCM (internal fault, water intrusion)
- Network bus not properly terminated or bus wiring shorted to battery/ground
- Other module(s) interfering with or taking down the bus
Symptoms
- MIL or dash warning indicating communication error
- Multiple modules inoperative or unresponsive (locks, windows, interior lights)
- No response from BCM in scan tool (module not present)
- Intermittent operation of body functions (lighting, locks, wipers)
- Vehicle may not start or accessory functions fail if BCM supplies power distribution
What to check
- Connect a factory-level scan tool and list stored/active codes; note any other communication codes (U-codes)
- Verify BCM presence on network via scanner (module detected or not)
- Check battery voltage and state of charge; confirm charging system output
- Inspect fuses and BCM power/ignition relays for continuity and proper operation
- Visually inspect BCM connectors and wiring for corrosion, bent pins, water intrusion, or damage
- Check BCM ground(s) for good contact and low resistance to chassis
Signal parameters
- CAN bus idle (recessive) voltages typically ~2.5V on CAN_H and CAN_L (measure to chassis)
- Dominant states: CAN_H rises ~+1V and CAN_L falls ~-1V producing ~2V differential (use oscilloscope to verify frames)
- Low-speed GMLAN may be a single-wire bus—refer to service info for expected idle voltage and pulse characteristics
- Typical CAN bus bit rates: 250 kb/s or 500 kb/s depending on vehicle (confirm with service data)
- Check for short to battery or ground on bus wiring (low resistance or clamped waveform)
Diagnostic algorithm
- Record all DTCs and freeze frame data with a scan tool; note any U-codes indicating wider network loss.
- Verify battery voltage >12.4V with the vehicle at rest; charge if low and re-check communications.
- Inspect BCM fuses and relays; replace or bench-test as needed.
- Visually inspect BCM connector(s) and harness for corrosion, water damage, pin damage, or poor mating. Repair as needed.
- Verify BCM ground(s) have
- With key on (engine off), use a DVOM to measure CAN_H and CAN_L (or single-wire GMLAN) at BCM connector pins and compare to expected service voltages. If voltages are shorted or absent, isolate wiring.
- If voltages look normal, use an oscilloscope to view CAN waveforms while waking the network; look for valid frames or collisions/noise. Identify which segment is failing.
- Disconnect suspected aftermarket devices or modules added recently; verify if communications restore.
- Use wiring diagrams to isolate open/short by disconnecting sections or modules and re-checking bus status (start at modules closest to BCM).
- If wiring and power/ground are good and the BCM still does not respond, consult service information for BCM reprogramming/updates. If replacement is required, follow manufacturer programming and calibration procedures.
- After repair, clear codes and perform a full network scan and functional test of body systems.
Likely causes
- Blown fuse or faulty BCM power relay
- Corroded/loose BCM connector or ground strap
- Damaged CAN bus wiring (pinched, chafed, rodent) causing open/short
- Faulty BCM hardware or water damage
- Aftermarket device connected to CAN/GMLAN causing bus errors
- Vehicle battery low or poor charging causing modules to drop offline
Fault status
Status
BCM network communication lost — Body Control Module not responding on vehicle data bus.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
HUMMER
-
HUMMER: 2009
-
HUMMER: 2008
-
HUMMER: 2007
-
HUMMER: 2005
-
HUMMER: 2004
-
HUMMER: 2000
-
HUMMER: 1999
-
HUMMER: 1994
-
HUMMER: 1993
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email