check engine light turns off by itself without repair being made?
 

I have a 2005 C-240 with 36,000 miles. I brought it in as the check engine light came on. I was told I needed a secondary air injection module, and quoted a price of about $1,300. I decided against doing the repair right away (I wanted to look on-line and get more info before spending that amount of money.) In any event, the light went off by itself within a couple of days. wondering if that's abnormal...I see here that that repair code doesn't necessarily mean the pump is bad, but could be a hose or a wire (would the technician's check that, or would the shop automatically default to "you need a new air injection pump"?) thanks for your help!