Code
B2743
HUMMER
B — Body
Body Control Module — Input/Output Fault
AI status
Completed
Completed
100%
Causes
- Damaged or corroded connector or wiring at the BCM
- Open, short to ground, or short to battery on an input or output circuit
- Poor power supply or ground to the BCM (blown fuse, loose terminal)
- Water intrusion or physical damage to BCM or harness
- Intermittent or failed CAN/LIN communication to BCM
- BCM internal electronic failure or corrupted software
Symptoms
- One or more body functions inoperative or intermittent (door locks, lighting, wipers, windows, HVAC blowers, etc.)
- Illumination of dash warning lamp(s) related to body systems
- Erratic operation of relays, lamps or motors controlled by the BCM
- Difficulties with remote/keyless functions or central locking
- Possible parasitic battery drain when vehicle is off
- Communication errors on scan tool (lost messages or timeouts)
What to check
- Retrieve all stored and pending codes and freeze frame with a scan tool; record related U- and B-codes
- Inspect BCM connector(s) and wiring for corrosion, bent pins, damaged insulation, or water entry
- Check BCM power supply fuses, fusible links and relay operation
- Verify good battery voltage at BCM power pin(s) and continuity of ground to chassis
- Scan for CAN/LIN communication faults and verify bus voltage levels (approx. 2.5V idle, differential behavior during activity)
- Wiggle test harness while observing live data or module status to reproduce fault
Signal parameters
- Primary supply voltage to BCM: ~12V (battery present), no large voltage drop under load
- BCM ground: near 0 ohms to chassis/negative battery terminal
- CAN Bus idle voltage: ~2.5V on CAN H and CAN L midpoint; differential ~0V idling, pulses under activity
- Typical logic I/O levels: 0V (ground) for low, near battery voltage or 5V for high depending on circuit — reference vehicle wiring diagram
- Output driver current: should not be driving excessive current (compare measured current to specs for lamps/motors)
Diagnostic algorithm
- Connect a capable scan tool, read and record all codes (including U-codes) and freeze frame data. Note conditions when the fault set.
- Clear the code and attempt to reproduce. If intermittent, perform wiggle tests and monitor live I/O data while actuating related switches.
- Visually inspect BCM connectors and pigtails for corrosion, water intrusion, pushed‑out pins, or signs of arcing. Repair or clean as required.
- Verify BCM power and ground circuits: check fuses, relays, measure battery voltage at BCM supply pin(s) with ignition off/on and during operation. Repair poor connections.
- Check communication lines: measure CAN/LIN voltages and verify module presence on network via scan tool. Repair wiring or terminate faults on bus.
- Isolate suspect input or output circuits per wiring diagram. Backprobe and measure signal at BCM connector while operating the circuit to confirm expected logic levels and continuity.
- If an output is shorted, disconnect the load and check if the fault clears; repair or replace the defective load or wiring.
- If wiring and external components are good, consult wiring diagrams and consider BCM internal failure. Check for available software updates or reflash procedures before replacement.
- If replacement BCM is required, follow proper programming/configuration and immobilizer pairing procedures. After repair, clear codes and verify full system operation and no reoccurrence.
Likely causes
- Loose, corroded or bent pins in BCM connector
- Shorted output (lamp, relay, actuator) drawing excessive current
- Open input switch or intermittent sensor ground
- Failed BCM transistor or driver stage for an output
- Faulty ground or battery feed to BCM
- Recent body wiring repair or aftermarket device installed without proper protection
Fault status
Status
Stored when the Body Control Module detects an input or output circuit behaving outside expected parameters (open, short, intermittent, or communication loss). The code indicates a fault in the BCM I/O subsystem but does not by itself identify whether the cause is wiring, an external device, or the BCM itself.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
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Repair manuals
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138
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