I have an "engine light" problem that appears to be unsolvable. The underlying problem is the diagnostics capability. The dealer tells me that he cannot access the diagnostics. No codes, no nothing. He simply states that his computer will not register when attached to my car. I've had it back twice for the same problem with zero results. He states that his computer is able to "talk" to other 1996 E320s, but not mine. Help.