If your car is 1996 or newer you can get an OBD II scanner from Harbor Freight. Check here:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94169

It often goes on sale on the their website for $39. If you print a copy of the online ad and take to the local store they usually honor that price. Regular price is $59 but maybe it's gone up in the last year.

Their are a large number of codes. Those that begin with a zero are generic for all cars. Those that begin with a 1 are model specific (ie Mercedes). Assuming your CEL is not on you may have pending codes. Use the scanner to clear them and wait to see if they return. If they do investigate.

Knowing the code(s) and their description often is not enough. Post any codes you have out here for help interpreting them. Good luck.