Intermittent check engine light
 

On my 2008 W211 E320 Bluetec, for the last year my check engine light intermittently comes on for a few hours/days then turns off for a few days/weeks. When I took it to the dealer, they found no error codes stored other than signs of low voltage occasionally. I have replaced the primary battery. Any other ideas?

Thanks.

O2 sensors

If you really think it is power related it could be Voltage regulator or whole alternator or of course a bad wire somewhere. I doubt that it is power related and the dealer probably was reading a very old code.
When you use star and read codes it will show you codes that could be years old vs days so it is a guessing game. It does tell you if it is a current code or a not current code. I have found dealers love to leave old codes after fixing something so when I hook up cars to star they have codes that I or the car owner knows are years old. So if your car is throwing a CEL it will be in the history. What I would do is get a scan tool and next time the CEL pops up scan it right away and see what it is.