U0140 – Data bus: body control module (8CM)- no communication

Reinier

By Reinier (Contact Me)
Last Updated 2018-03-12
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
U0140 Data bus: body control module (8CM)- no communication Wiring, failed control modules, switches, sensors, actuators, or locking mechanisms in any BCM related system, PCM

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What Does Code U0140 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.

Where is the U0140 sensor located?

The image above shows a simplified schematic of some of the major systems and functions that are typically monitored /controlled by the body control module.

Note however that although the actual location of the body control module varies greatly between applications and even models, it is commonly located behind/under the dashboard, or in the center console, but sometimes also under a front seat. Refer to the manual for the affected application to locate and identify the body control module correctly, since it is easy to confuse the PCM and body control module on many applications.

What are the common causes of code U0140?

It should be noted that while body control modules do fail, the most likely cause(s) of this code are more likely to involve wiring issues and/or poor connections than a failed control module. Be aware that the CAN bus system as it relates to the body control module consists of hundreds of circuits that are all interconnected. In practice, this means that unless the cause of this code is obvious, such as a melted wiring harness, diagnosing this code may require testing each circuit individually across several hundred connections in dozens of connectors.

Therefore, non-professional mechanics should take note that if this code is present on any application, it is almost invariably more prudent and cost effective to refer the application to the dealer or other specialist repair facility for professional diagnosis and repair. Note that in some cases, repairs could include replacement of the application’s entire wiring system as a cost (and time) saving measure.

Nonetheless, some common causes of code U0140 could include the following-

  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors almost anywhere in the CAN bust system
  • One or more defective or failed control modules
  • One or more failed control switches, sensors, actuators, or locking mechanisms in any system that is controlled or monitored by the body control module
  • Failed or failing PCM. Note that this is a rare event, and the fault must therefore be sought elsewhere before any control module is replaced

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