With some codes, the only way you can find what they mean is to use google (or duck-duck-go) and enter:

Mercedes SLK320 Pxxxx code
For an SRT, change it to "SLK32AMG".

While our list of DTCs here on this site works for most codes, we are missing some. Also, I find that reading several links (NOT just one site's text) that result from the search will usually teach me a lot abotu how to interpret what could set that particular code off. Just always keep in mind that your car is a 2003 Mercedes SLK320 with a few "tweaks" that set it apart from a REAL SLK320; but most of the time, the SLK320 answers apply to your car.