Check engine light can go on for a variety of reasons, gas cap is one of the easy ones. O2 sensors (before and after Cat) can trip it. Did you get the OBD code? Which sensor did they tell you was bad? You can also disconnect the battery for a short period of time and reset the system. However, if the sensor is in fact bad, the light will only stay out for a little while until the system BIT is complete.
Clay - I could KISS you (but my hubs and your wife may not approve!) Friday's check engine light was due to them damaging the grounding pin on the o2 sensor when they replaced the engine mounts. So it could be possible that the o2 sensor is to blame? They didn't replace the sensor - they just "fixed the pin" (that's what he told me) The code tells them to replace the charcoal filter and cvs valve because "there is a leak" - not that they've verified it - but that's what the code says to do.
The service manager is out until Thursday - DH & I have been googling for info - it's crap that they did something and want to charge me $370 to fix it. The service guy actually told me this happens due to age - umm, yeah I get that, but 2 check engine lights in 2 days...not a coincidence when they occur 24 and 48 hours after major servicing. And they wonder why I stopped taking it to them to begin with.
DH did tell me he was wrong and I was right today though ;-) I wanted to take it to our normal mechanic - he wanted to take it to Honda since they would know more about their transmissions - yeah *snort* the transmission they told me to avoid driving 35 mph if I wanted the shudder to stop. arses.
The code from Friday was for a loose ground pin at o2 sensor (didn't give me the actual code)
The code today (I drove it home Friday and didn't drive again until this morning) was 2705 off, 2693, p1457
It's adorable! The dual coil carto is almost bigger than the PV! 
