1991 BMW 735iL Body Control System Diagnosis & Testing Cost

Older vehicles had few accessories and electrical components, so computerization was not needed. Manufacturers were able to use a small wiring loom, or wire harness, to make every connection to every electrical component in the vehicle. While newer vehicles have many of the same systems, we demand more from our vehicles in terms of convenience, security, performance, emission reduction and functionality, so hundreds of additional electronic components are now added to each and every vehicle manufactured. The majority of vehicles see this increase in the engine bay, and these components are likely emissions related. However, when comfort, performance, functionality and security are added, the list of electronics piles up quickly - as does the need to manage these systems. Enter the body control system. It is comprised of all functions of the vehicle, devices to link those functions, and processing units to control those functions.

This system, for all intents and purposes, controls every function of the vehicle in some way. For instance, the doors may lock from a button, but they also lock when the vehicle hits a certain speed or unlock when the shifter is placed in park. This is accomplished because the body control module has information from the transmission position sensor, door lock switch, vehicle speed sensor, and the individual door locks. So when the doors are locked with the switch, the body control module is taking the same action it does when the speedometer reaches a select speed. This being the case, it must be understood that each function of the vehicle which cause the doors to lock, including pressing the switch, is actually a communication to the body control module. When the body control module gets this signal, from any of its' sources, it will take the action to lock or unlock the doors based on its programming. This process is the same for all aspects of the vehicle. Some of which may be the headlights, anti-theft system, ignition switch, and many others.