What does it mean?
OBD II fault code U0144 is a generic trouble code that is defined as “Lost Communication with Body Control Module “D”, and is set when the PCM (Powertrain Control Module) detects a break in communication between itself and the BCM (Body Control Module). In some cases, this code will also set if a break is detected between the PCM and other control modules that communicate with the PCM via the BCM over one or more serial communications networks.
Modern vehicles can contain several dozen control modules that collectively, control, monitor, and manage every aspect of the vehicle’s operation. In practice though, some modules are dedicated to specific functions, such as the BCM that is limited to controlling functions that include but are not limited to, climate control, power window/seat adjustment, interior lighting, and others.
Which specific functions are controlled by the BCM on any given application depends on the vehicle, and that particular models’ trim level and fitted equipment. Nonetheless, the PCM on almost all vehicles act as a sort of clearinghouse for all communications, including communications to and from the BCM from other control modules.
We need not delve into the complexities of modern serial communications systems here, beyond saying that many of the communications that Body Control Modules both transmit and receive are shared by various other control modules, including the PCM to verify the overall integrity of all serial communications systems. One particular example of why stable communication is required between the PCM and the BCM involves climate control.
Since the operation of the climate control system has a direct bearing on engine performance, the PCM needs to know not only the status of the climate control system but also the various settings of the system so it (the PCM) can make appropriate adjustments to, for instance, the idling speed to prevent the engine from stalling during idling.
There are many other possible examples, but the point is that for the PCM to control and monitor the myriad functions that keep modern vehicles operating safely and reliably, it needs to have uninterrupted access to all communications between all control modules over all active communications networks.
Thus, if a break in communication between the PCM and the BCM occurs, the PCM will recognize that it cannot control, monitor, manage some of its own, specific functions, and/or monitor the functions of other control modules, and it will set a fault code as a result. Note that depending on the application, warning lights may not be illuminated immediately, or may not be illuminated at all.