Posted by S-TEE on December 18, 01 at 19:19:10:
Just thought I'd make a follow-up on a problem I was having...
I have an '01 Denali XL that would get a Service Engine Soon (SES) light occasionally. I seemed to be getting the SES whenever I was at about a 1/2-tank of gas, in a deacceleration mode after steady 70-80 mph driving. I had installed a Stant locking gas cap that I had used on my '96 Tahoe. The first time it happened I tightened the cap, but still did not get a self reset. On-Star remote diagnosis had just a general "emission or fuel system" cause. Dealer tech verified it was a evaporative system code, and went straight to the gas cap. Reset the light, and all was fine. Couple of thousand miles later I had a similar set of conditions, and the light came on again. This time it reset itself after 3 days.
Fed up with this, I went and bought a GM locking cap--and soon had a SES indication. Dealer reset light. Told him I would try one more time, then go back to stock. Well, it went on again--always in a deacceleration mode, after high speed driving, with about a 1/2-tank of gas. About this time, I happened to tallk to a dealer pal--and he told me that there was a bulletin issued a couple of years ago to NOT use the cap, due to SES indications! Figures that parts dept. would still sell it to me, or that nobody else knew anything about it!
So now I am back to using my stock unlockable gas cap, and it looks like the problem is finally gone. So, if you have a later model vehicle, be aware that SES indications may be due to using a locking gas cap, or even a loose stock gas cap...