Lots of misinformation in your story. First of all, you are wrong about the mechanic damaging the Body Computer. While it is possible to intentionally do that, it would take a lot of effort to purposely do something like remove wires from the connectors and reattach them in the wrong order.
Second, it's highly doubtful anyone would get an Engine Computer with a "cracked board". They are sealed in a protective jelly inside the housing and are real hard to get out. I've taken some out to purposely damage one tiny circuit to create problems for my students to diagnose, and it's not an easy job. The boards are really tough and almost impossible to break. If one would be cracked in a previous crash it would have been rejected by the rebuilder and it certainly would not have passed their performance checks. If this was a used computer from a salvage yard and it came from a vehicle that was in a crash there would certainly be evidence of that on the housing.
Third, computer and other electrical problems will not cause physical damage to the transmission. When an electrical problem occurs the system will put the transmission into second gear and it will stay there until you turn the ignition switch off and restart the engine. A physical problem will not result in the speedometer quitting. That points to an electrical problem.
You have a bunch of electrical problems in all different circuits so I would start by looking for things they all have in common. Since the Air Bag light turned on, check that computer for diagnostic fault codes. Those may give a hint as to the cause. The Body Computer talks back and forth with the instrument cluster, which is also a computer module, and either one could be responsible for the warning lights in multiple circuits turning on.
It's interesting too that the transmission problem you described was supposedly fixed once by rebuilding it, then fixed for the same thing by replacing the Engine Computer. Instead, start with some more common things like a defective alternator. Have it load-tested to see what it will deliver for maximum current and "ripple" voltage. If it will only deliver exactly one third of its design rating for current and ripple is high, it has a bad diode. 35 amps from the common 100 amp alternator is not enough to meet the demands of the electrical system under all conditions. Computers hate low system voltage and excessive ripple, (variations in voltage), and they'll do weird things, like turn on warning lights, and turn things on and off.
Also look at the smaller battery wires where they attach to the under-hood fuse box and body. Those often become loose on any brand of vehicle and cause intermittent no-start conditions to flashing dash lights while driving. Those are a couple of examples of things that are in common with all the systems you're having trouble with.
Tuesday, June 18th, 2013 AT 10:32 AM