Troubleshooting tip
If you recently purchased gas for your stang, check to ensure that the gas cap is screwed in securely. If not secured tightly, this can sometimes cause the "Service Engine Soon" light to come on. Hopefully it's a simple fix like this & not some expensive engine problem.
FYI: California does have lemon laws on the books to compliment the Federal lemon laws. If you continue to experience problems with the dealership regarding your purchase, you may wanna consider checking into them.