What does it mean?
OBD II fault code U0140 is a generic code that is defined as “Lost Communication with Body Control Module”, but sometimes also as “Data bus: body control module (8CM)- no communication” and is set when the PCM (Powertrain Control Module detects a communication failure between itself and the BCM (Body Control Module) via the CAN (Controller Area Network) bus system.
In simple terms, the body control module monitors functions and systems on the application that do not involve management of the engine, fuel system, or the operation of the brakes and the transmission.
In practical terms however, the body control module controls functions such as the operation of the door power locks, power seats/windows, automatic wipers and/or rain detection system, interior/exterior lighting, security/anti-theft system, infotainment system, restraint systems such as seat belt tensioners and air bags, and many others.
In terms of operation, the body control module is connected to all the systems it controls/monitors, as well as some other control modules via the CAN bus system, which is a high-speed serial communication system that allows all connected control modules and systems to share information and commands during normal operation of the vehicle.
Note that all connected control modules contain pre-programmed information (including information that identifies the transmitting module) that is shared with all other connected control modules. Put in another way, each module expects to receive this information periodically from all other control modules on a specific network as a means to verify that both the transmitting and receiving modules are performing as expected.
This exchange of information is monitored continually, and should the PCM detect a break in communication between itself and any part of the system that is controlled by the body control module, it will set code U0140, and depending on the application and the nature of the failure, may also illuminate a warning light. Note that on most applications, this code will set when a break in communication exceeds about 250 milliseconds, although this period of time may differ between applications.