Follow all of the above, most importantly check your oil and check for oil leaking out. Don't be surprised if its simply low on oil. Most oil change shops aren't used to car engines that hold around 9 quarts of oil. That's double what they are used to, and their reference literature is often wrong.
Pure guesswork here on my part, but I'm thinking that you didn't tell GF to take your 500 to a Jiffy Lube (?). If you didn't, I'm also guessing that the appearance of the oil light prompted the visit?
If your oil level is good, check your fuses for hair line cracks or other areas of poor contact. Better yet change them all out if you haven't lately. There are threads here that talk about these old style ceramic fuses and the endless mischief they cause. A fuse issue could also be causing your ACC difficulties.
Other possibilities include the known issue of wiring harness disintegration, in this case the lower engine wiring harness (sometimes called the "starter harness").
In very rare but increasingly frequent instances, the float in the oil level sensor simply looses buoyancy and refuses to float high enough in the fresh oil, as the fresh oil tends to be less dense. Some modern oil formulations are less dense in use as well. If this level sensor fault is happening it tends to show up right after an oil change. Really helps with customer relations, I'll tell you...
The following has nothing to do with your low oil warning light, but after that issue is resolved, consider having your oil filter checked and replaced by an OEM part unless you know first hand that that's what they used! See the related oil filter threads. Here's why I'm mentioning the filter element: Lots of these oil change shops are using some very low quality third world sourced filter elements. After a few thousand miles, some of them are literally in pieces. Don't let your engine run with one of those any longer than absolutely necessary.
