I love my 850 for the onboard diag ports that let me not only read the check engine light but the SRS and ABS lights along with being able to reset them. It's brilliant and something all manufacturers should be mandated to do. That being said for those of you that don't have that capability or if you need an explanation of the number these two auto parts stores will let you take their fairly expensive scanners out to the parking lot to use to read and reset your codes FREE.
The units they loan are dirt simple and for a little effort finding your diagnostic port which is usually just under the dash on the drivers side (mine is just above the shifter near the lighter) you save going to a shop and paying $$$.
All you do is plug it in, turn the ignition to on so the idiot lights come on and press a button on the scanner to read. That's it and you solve the what the heck is that light on for question and get information you can use to decide to fix it yourself or take it in.
This is just a heads up as I'm surprised daily on how many people don't know this is available and it's FREE! I just love free.
I'm not sure on AutoZone, I know theirs does the check engine light but O'Rielly recently added one that will do CEL and the Antilock.

 

I've been going to autozone for over a year now. best incentive to shop there.

 

Also a Calif resident, if you are lucky and they do read it for you they will not reset it. Just buy your own and then charge people $5 to read their codes. You'll have it paid for in no time. Not knocking Autozone, love the place.