ABSTRACT
When Bob bought his new 2000 Cadillac Sedan DeVille DTS (Figure 1.1), one of the first things he wanted to do was upgrade the factory sound system. He took it to Kenney’s Allston shop, Sound in Motion, and selected a new head (radio) and asked Derek Kenney to install it in the new car. When Kenney completed the removal of the factory radio and installed the new head, the new system sounded great. However, he soon discovered that pulling out the original radio resulted in the car’s air conditioning, alarm, and computer diagnostics systems to stop working. The only way Kenney could get the new head to work without disabling the A/C, alarm, and computer diagnostics was to install the old radio in the trunk. “The guy actually has two radios in his car, one he listens to and one to keep the car working,” Kenney said.*
What happened? When the A/C engineers were designing their system for this vehicle, they needed a little more processing power and noticed the radio had excess capacity in its electronic control unit (ECU). Rather than adding another ECU for the A/C, they used the excess capacity of the radio, thus tightly coupling the radio with the A/C. The same approach was used when the computer diagnostics engineers needed a bit more capacity for the alarm system. The result? Four unique subsystems, that have no relationship to one another, became tightly coupled. Whether that was to save a few cents in production costs or not, it represented a lack of a systems view-someone not watching each of the parts in the context of the whole. In the end, the old radio ended up in the trunk just to keep the car running properly.
