You need to read the codes causing the CEL and take it from there. CEL comes on for many reasons, one of them being the loose gas cap (or no gas cap in your summer adventure). This is probably unrelated to the gascap incident and needs to be treated as such. You can buy an OBDII scan tool and read/clear the codes yourself, but some of the codes your Volvo stores may not be readable by a genegric OBDII scanner, since they are proprietary Volvo codes. I was having a recurring CEL with Volvo codes 611 and 612 (fine and gross leak in the fuel evap system - typical gas cap codes, but in my case turned out to be a faulty gas tank). My generic OBDII scanner was not able to read the codes, but was able to reset them.

Hope this gives you some information to go on.