CPU is in the LDU which is usually at the top floor door buck. The CPU is called CANMB. You'll need a goofy round barrel key to open the unit. Or a small screwdriver works well. The board at the top with the display is the CPU. I'd be here for a month of Sundays telling you how to test these. It isn't a system friendly to a novice. You'll need a manual and a test procedure book.
