Hi I was wondering if anyone can give any insight on my problem.

I have a 95 E420 and the check engine light came on after I started the car. It does not have any power loss and the engine seems to behave normally. I set up an appointment to get it diagnosed but the light went off before I could even go. Then 2 days later it went on again.

a. Is it normal/common for the CEL to turn on and off intermitently?
b. Is the car able to self correct the error?
c. I have read that Auto Zone does the diagnostic for free - how reliable are they compared to the dealer ($100+ per visit) diagnostics?

95 E420
135,000K

I would appreciate any comments or suggestions.