Having repeated problems with a check engine light coming on, and not being resolved by my mechanic.

So I have two questions:

1) Does anyone have the check engine light diagnostic codes for a 1991 420 SEL? (Codes given for other models, but not the 420).


2) On the 91' 420 SEL, does the checking of the codes require special diagnostic tools to check or, like I've read in other posts, is there a LED light flash that can be counted? If so, where do I find the LED?

Thanks in advance for any info.

(And this a great forum, not sure what I'd do without it...)