What might cause my 2010 Audi Q5 check engine light to come on?

There are a myriad of reasons why the 2010 AudiQ5's check engine light would come on, and it's impossible to narrow down for You unfortunately. The check engine light acts as a sort of "catch all" for diagnostic trouble codes, which are readable with an OBD-II scan tool. It just tells You that You need to harvest Your code(s) -- it won't point You to a specific problem without them. Common causes include a failed fuel pump, a loose gas cap, an EVAP emissions leak, faulty spark plugs, or any one of a number of sensors that has failed. In order to narrow down, You can search Vehicle History or another site with the DTC information You get from Your OBD-II; if You don't have one, they'll typically scan Your vehicle free of charge at most major automotive part stores.