Code
B0738
HUMMER
B — Body
Body Control Module internal fault
AI status
Completed
Completed
100%
Causes
- Internal BCM hardware failure (processor, memory, internal power regulation)
- Corrupted or failed BCM software/calibration
- Low or unstable battery/vehicle supply voltage during programming or operation
- Poor power/ground connections or corroded BCM connector pins
- Water intrusion or physical damage to the BCM housing
- Intermittent or shorted wiring on BCM power, ground, or network lines
Symptoms
- Malfunction of multiple body functions (lights, wipers, door locks, HVAC blower, etc.)
- Warning lamps or message center indicating BCM fault
- Intermittent or complete loss of communication with BCM on scan tool
- Accessories not responding or behaving erratically
- Vehicle may not go to sleep or may have increased battery drain
What to check
- Scan for all stored and pending DTCs and freeze frame data; note related network/communication codes
- Verify vehicle battery state of charge (12.4–12.8 V resting) and charging system operation (approx. 13.5–14.8 V with engine running)
- Inspect BCM connectors and harness for corrosion, bent/broken pins, water intrusion, or physical damage
- Check fuses and relays feeding the BCM and related circuits
- Measure BCM supply voltage and ground(s) at the module with ignition off and on
- Check CAN/LIN bus continuity, resistance and for shorts to power/ground; verify termination resistances
Signal parameters
- BCM supply voltage: ~11–14.5 V (ignition OFF/ON as specified by factory)
- Ground resistance: should be low (
- CAN bus idle differential: approx. 2.5 V each line (approx. 2.5 V on CAN_H and CAN_L center)
- CAN bus differential voltage during traffic: ~2–3 V peak-to-peak
- LIN signals: sleep/wake logic levels per factory spec (usually 0 V and battery voltage levels)
- Quiescent BCM current: compare to factory spec (excessive current may indicate internal fault)
Diagnostic algorithm
- Connect a diagnostic scan tool; record B0738 and any other codes, note occurrence conditions and freeze frame data.
- Verify battery charge and charging system. If battery low, charge and recheck codes after normal supply restored.
- Visually inspect BCM connectors and harness for corrosion, water entry, or damage; repair any harness/connector issues before further testing.
- With key off, measure BCM supply voltage at module connector and check primary ground(s). Repair poor power/ground as needed.
- Check CAN/LIN network integrity: scan tool communication with other modules, check termination resistances, inspect for shorted wires or intermittent connections.
- If supply, ground, and network OK, attempt a soft reset/restart of BCM per factory procedure (allow sleep, battery disconnect if permitted by factory).
- Reflash or update BCM software/calibration to the latest factory level using OEM programming tools if available; recheck for recurrence.
- If code persists after proper programming and verified vehicle wiring/power, consider module replacement. Confirm replacement module is programmed/configured to vehicle (VIN, options) per factory procedure.
- After repair or module replacement, clear DTCs and perform functional tests and a road test to confirm issue is resolved.
- If intermittent or unresolved, capture data during failure (scope/record CAN traffic, voltage logs) and consult OEM technical support or TSBs.
Likely causes
- Corrupted BCM calibration or failed reflash
- Faulty BCM power supply or ground connections
- BCM internal component failure after moisture exposure or electrical surge
- Intermittent CAN/LIN bus fault causing internal error state
Fault status
Status
B0738 - Body Control Module internal fault detected. Internal memory or processor error; module may require reprogramming or replacement.
Repair difficulty: Hard
Diagnostic time: 2.0-4.0 hours
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138
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