Summary
U0140 indicates that a control module has lost CAN bus communication with the body control module (BCM). The BCM manages lighting, power windows, door locks, wipers, horn, and many other body electrical functions. The most common causes are corroded BCM connectors (~30%), CAN bus wiring faults (~25%), and water damage to the BCM itself (~20%). Symptoms vary widely depending on which functions the BCM controls on your specific vehicle — anything from dead power windows to inoperative headlights.
Severity: Moderate to High — affects multiple body and convenience systems
Safe to drive: Yes, with caution — but headlights, wipers, or turn signals may not work
Repair cost: $100–$800 depending on cause
DIY difficulty: Moderate
What does U0140 mean?
The body control module (BCM) is a central computer that manages the vehicle's body electrical systems. Depending on the manufacturer, it may control exterior and interior lighting, power windows, power locks, keyless entry, wipers, horn, chimes, power mirrors, heated seats, and even the security/immobilizer system. The BCM communicates on the CAN bus to coordinate with the ECM, instrument cluster, and other modules.
U0140 is set when another module (typically the ECM or gateway module) stops receiving expected CAN messages from the BCM. This indicates the BCM has gone offline — it may have lost power, its CAN bus connection is broken, or its internal electronics have failed.
On most vehicles, the BCM is located inside the passenger compartment — commonly under the dashboard on the driver's side, behind the kick panel, or inside the center console. While this location protects it from engine bay heat, it can be vulnerable to water intrusion from windshield seal leaks, sunroof drains, or HVAC condensation. Water damage to the BCM is one of the most common causes of U0140, particularly after heavy rain or car washes.