No manufacturer gives out the schematic diagrams for their computers like we can buy for tvs and vcrs. What your mechanic is probably referring to is the wiring diagram for the wires going to that module. That is part of the diagrams in the service manual. All shops have paper manuals or they subscribe to very expensive online service manual companies. You can buy a one year subscription for one vehicle but that is not practical. First of all, would you know which of the hundreds of pages to print out? Second, Chrysler diagrams send you to all different pages for different parts of the circuit. For sure you'll end up missing a few important pages. Third, I never heard of a shop requiring the car owner to supply the service information. That's part of why they have to charge so much to look at your car. Subscribing to online service literature is one of the expenses of running the business.
The next problem is no one is going to know which part is defective on the module, (assuming one is), and they won't be able to buy a replacement part anywhere. The only thing people like me can do is look for broken solder connections and repair them. We do that all the time in car radios and tvs. In this case, however, you're talking about a very low-level module that is expensive to buy new, if you still can, but very inexpensive to buy used from a salvage yard.
The first thing to do is check for 12 volts to the computer. Without even searching for a diagram, there must be one wire that has 12 volts all the time to maintain the memory, and another one with 12 volts with the ignition switch on to turn on the display. There will be a ground wire too but we already know that is working because the overhead lights share that wire and those are working. If the two 12 volt wires are good, suspect a problem on the module. You'll find all kinds of them in the salvage yards because they were a very low-failure item. Look for a yard where you take your tools and pick your own parts. If you're anywhere between Ohio and southern Georgia, there is a real nice chain of yards called "Pull-A-Part" where you pay your buck, throw your tool box in one of their wheel barrows, and you can spend all day there. Parts are real inexpensive, customers and employees are very friendly, and the yards are all very clean and well-organized. My list is a few years old but a computer module was listed at 27 bucks. What you need falls under a different category for which I paid 18 dollars for a module a couple of years ago.
Normally we hate just throwing random parts at a problem hoping one will fix it, but with this type of problem it is a real easy and fast test to just pop in a replacement module. If it solves it, you're done. If it doesn't, at least you know right away the problem is in the wiring or a blown fuse and you know where to start with the diagnosis.
Thursday, June 27th, 2013 AT 4:40 PM