You've added a few details that made me rethink my response. If tapping on a computer makes it change its behavior, that is indeed a potential sign of a bad solder connection inside but first I'd rule out loose or corroded connector pins. Those terminals are pretty tough and they're well-sealed so the few times I have actually found a problem it was after someone was working in the area or had that connector apart.
Most of the time new computers are very expensive so it's customary to get rebuilt units, even through the dealer. I worked for a very nice Chrysler dealership all through the '90s and the only times we got brand new computers was when the vehicle was under warranty and Chrysler was paying the bill. When customers were paying the bill we always installed rebuilt, (remanufactured) computers to save money, and I don't recall ever having a problem.
There's a lot of computers on your vehicle and they all talk back and forth to each other over two wires called the "data buss". You can't damage one computer by having another one send out harmful information on that data buss. That's why I'm looking for a different cause for the multiple problems, and the charging system is the one that is responsible most often. GM owners know more about that because they have a huge problem with their generators developing voltage spikes that cause damage and interfere with computers and their sensor signals. ("Generator" is the new industry standardized term. The common term is "alternator" but that was actually used first by Chrysler in 1960 and they copyrighted that term).
There really isn't anything simple a mechanic can do to accidentally damage a computer. All mechanics live in constant fear of parts failing while we're working on the vehicle, then having to explain that to the owners, but it happens quite often. I run into that with some of the radios I'm asked to fix and there is one specific problem that DOES occur when the mechanic has to disconnect the battery. When he reconnects it later is when the radio is dead, so of course the owner "knows" the mechanic caused the problem, but I have the service bulletin that explains how the problem actually developed months or years earlier. It just won't show up until power to it is disconnected for a while.
That's one example of what I mean by living in fear of something breaking while we have your car. Most such problems are more varied and random. I would be suspicious too, but when that happens to my vehicles it's me who is working on it so I don't have to worry about who gets the blame.
I don't have a good answer about how they did the diagnostic tests and what would show up. We rely pretty heavily on diagnostic fault codes that can be set and stored in every computer. A lot of codes point specifically to an internal failure inside a computer but most codes relate to external sensors and actuators or the wiring to them. In the absence of any codes, about all you can do is condemn a computer if it isn't performing the proper functions. My concern is there is an underlying cause in a different circuit that got overlooked and is causing the incorrect behavior. We never like throwing random parts at a problem, but in the case of a computer, if the problem goes away when you substitute a new one, that pretty much proves there is no other defect.
Wednesday, June 19th, 2013 AT 1:20 AM