OBD-II varients
 

I figured I'd pose this question to the POT brain trust....

My wife's 2001 Jaguar XJ8 is setting a CEL (Check Engine Light), but my OBD-II reader shows no codes. The reader will turn the CEL off, but the light returns a day later.

With great curiosity I've been searching the Web for an answer. It appears there is a CAN-OBDII "standard". When did this take effect? Is this why I can't display the code(s)? I have a non-CAN reader, and a CAN-OBII car?

Here's a link to various protocols http://www.scantool.net/browseCV.html
What kind of scanner do you have? It might be limited to various auto models?
CAN is an electrical field bus interface ( hardware) the "standards" that you refer to are protocols ( think telephone as the interface, but one of you is speaking french the other english). So if you can re-set a CEL with your scanner it's talking the correct language, just doesn't know a few words is my guess...

I have an Equuis reader like this one.

My reader is a snap-on, and honestly it doesn't have the Jag software, I would have to download it. I think its to get a scanner that you can plug into your pc and download the updates.

I had the "check engine" light come on in my BMW. I bought a $35 OBDII tool on eBay and it said I (edit - my car!) had an "evaporative emissions" problem, or something like that. The e46fanatics.com board said it was a bad gas cap.

Resetting the CEL worked briefly, then the light came back on. I bought a new cap from Pelican, then reset again and the CEL stayed off.

My point is, I think one needs to fix the underlying problem for an OBDII CEL reset to work, AFAIK.

Best,