Is the following possible?

[Da Dark Jedi]

About 4 weeks ago I put gas in my 97Q but didn't tighten the cap back. This condition produced a "Service Engine Soon", so I put about 60 or so miles thinkng it will reset and all will be well, but this did not happen. So the codes were pulled and it came back O2 sensor rear & Knock sensor rear, both on the same side. The car drives fine no trouble at all.

Now here is what just happen last week. The "Service Engine Soon" light went out, like it reset itself . Is it possible that the gas cap was not tighten that threw these codes ? Will these conditions come back later on?

[Victor]

The owners manual says a loose gas cap is one of the things that can cause a check engine light to come on. My daughter's 2000 Q45T did the same thing, with a code for the rear O2 sensor. I reset it once myself by disconnecting the battery. It came on a few weeks later and I had a mechanic reset it with a OBD2 code reader. On another board someone posted that the code for this fault is a false fault. My daughters car ran fine with the check engine light on too.

[MinisterofDOOM]

Loose gas cap can trigger an "EVAP" emissions code, which will trigger the CEL, and which will reset (and CEL will go away) once the car sees a good gas cap seal again. But it should not cause a knock sensor code or an O2 sensor code.

[mtzgr777]

When I first bought my Q (2 weeks ago) I filled it up with 91 Octane and on the way back home, the SES light came on stating a Knock Sensor malfunction and Idle Control problem. I put some fuel injector cleaner in it and then had Auto Zone reset it with their code reader. Runs fine, my only issue is passing emissions in a couple weeks....