Code
U0140
Generic
U — Network/User
Lost Communication With Body Control Module
Views:
UK: 27
EN: 54
RU: 88
AI status
Completed
Completed
100%
Causes
- Blown fuse or BCM power supply failure
- Poor or missing ground(s) to BCM
- Damaged or corroded BCM connector or wiring harness
- CAN/LIN network fault (short to battery/ground, open, high resistance)
- Missing or failed CAN termination resistor(s)
- Other module pulling the bus off or network collisions
Symptoms
- Scan tool cannot connect to BCM or shows U0140 stored
- Multiple body systems inoperative (interior lights, door locks, windows, wipers, lighting)
- Instrument cluster messages or warning lamps tied to BCM functions
- Key/immobilizer or remote entry may not work
- Intermittent or permanent loss of features controlled by BCM
- Other modules reporting multiple U-codes for lost communications
What to check
- Verify battery voltage is healthy (12.4–12.8 V at rest; >13.5 V with engine running) and battery terminals are clean/tight
- Check for relevant fuses/fusible links and relays for BCM power circuits; replace if blown
- Scan vehicle for additional U-codes and module communication status
- Visually inspect BCM connector(s) and wiring for corrosion, bent pins, damage, water intrusion or crushed sections
- Check vehicle grounds associated with BCM (measure continuity to chassis and battery negative)
- Measure for presence of key BCM power feeds (battery, ignition) at the BCM connector
Signal parameters
- CAN bus idle: both CAN_H and CAN_L near ~2.5 V (recessive)
- CAN dominant state: CAN_H rises to ~3.5 V while CAN_L falls to ~1.5 V during dominant bits
- Differential when active typically ~2.0 V (varies by system)
- Correct termination across CAN_H/CAN_L ≈60 Ω (two 120 Ω terminators in parallel)
- LIN bus (if used) typically idle at battery voltage with low pulses when active (varies by manufacturer)
Diagnostic algorithm
- Record all active and stored DTCs in all modules and note freeze-frame/occurrence conditions. Do not clear codes yet.
- Verify vehicle battery state and charging system. Reinspect battery connections and ground straps.
- Check BCM power and ignition feeds at connector for proper voltages with key ON and engine RUN. Check associated fuses/relays and replace if faulty.
- Inspect BCM connector for corrosion, bent pins, water intrusion and repair as needed. Wiggle-test harness while monitoring for communication changes.
- Use a scan tool to monitor CAN traffic. Confirm presence/absence of BCM messages and whether other modules can communicate normally.
- Measure CAN_H and CAN_L voltages with ignition ON and during attempted network activity. Compare to expected idle and dominant values.
- Check termination resistance across CAN_H and CAN_L (should be ≈60 Ω). If open or incorrect, trace/repair termination resistors or wiring.
- Visually and electrically inspect wiring for shorts to battery/ground or opens, focusing on harness routing and prior repair areas. Repair any damaged wiring.
- If bus shows severe errors or a module is bus-off, isolate modules by disconnecting suspected aftermarket devices or non-essential modules one at a time while monitoring the bus.
- If power/ground/wiring and bus are good but BCM remains non-responsive, check for available software updates or known BCM recalls/service bulletins and perform reflash per manufacturer procedure.
- If BCM still fails to respond after confirming proper power, grounds, and bus integrity, consider module replacement. Program/configure replacement BCM per manufacturer instructions.
- After repairs, clear codes, perform relearns/programming as required, and road test to confirm network stability and that U0140 does not return.
Likely causes
- Blown/loose BCM fuse or fusible link
- Battery low voltage or poor battery connection
- Corroded/loose ECU/BCM connectors or pin damage
- Open, shorted or chafed CAN high/low wiring near rear/front harness splices
- Failed BCM power or ground circuit
- Failed CAN termination (not ≈60 Ω across CAN_H–CAN_L)
Fault status
Status
Lost Communication With Body Control Module (BCM) — BCM not responding on vehicle data bus; body functions may be disabled.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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