Changed to Mobil 1 and P0421 disappeared

[CDub]

So I've had the P0421 code for a couple years now and haven't dealt with it, because I didnt notice any performance issues, and I wasn't looking forward to the potential of paying to replace a couple o2 sensors and a cat or two. (EDIT: for those who don't know, P0421 signifies that the readings from the pre and post cat o2 sensors are out of spec. Usually indicating a failed o2 sensor(s) and possibly a failed cat which = $$ to fix)

Yesterday I decided to change over to Mobil 1 synthetic high mileage thanks to some posts I read on the forums that said it was a myth that changing over from dino oil will cause seal problems.(Ken, your info in these threads was very helpful as usual...THANKS!) I started it up to move it from the garage so I could clean it up and didn't notice anything different. An hour or so later as I was driving out of my neighborhood I noticed that the check engine light was off. I figured it would come back on again in no time since its been on so long, but I've driven 50 miles or so since then and its still off.

Hopefully it stays off, and if it does, it must be a testament to the benefits of running Mobil 1. I don't want to look a gift horse in the mouth, but I'm wondering what would cause this to happen. My guess would be the additives in the high mileage formula. Anyone else have any ideas about possible reasons for this?

[yel-low]

Keep driving it will come back on. Your ecu reset. Pull the code. It is still logged in there.

[T2T]

Originally Posted by yel-low

Keep driving it will come back on. Your ecu reset. Pull the code. It is still logged in there.

How would the ECU have been reset by just changing the oil? Hmm ... ?

[yel-low]

No.
There are no feedback sensors in the oil system other than the "idiot" light.

[Goliat6288]

ECU resets by itself. it happened to me b4 with my O2 sensor. After 100 or so miles the light would come back on. Hope it doesnt for u.

[T2T]

If you've had on-going issues (CEL codes) for the pre-cat readings, have you considered the modification using the spark plug anti-foulers?

[yel-low]

Oil had nothing to do with it.

[ME2000]

Originally Posted by yel-low

No.
There are no feedback sensors in the oil system other than the "idiot" light.

I like idiot lights. They're very helpful...

[CDub]

Yel-low, consider these facts, my car does burn a bit of oil. It has also been running rich for a while. The light first came on right after I had a coil pack replaced meaning there was probably unburnt fuel in the exhaust stream. Because of this, the o2 sensor may have had fuel deposits on it; the burnt synthetic oil and its different additives may have cleaned said o2 sensor. This sounds completely logical to me...if I am missing something please let me know.

By the way, your posts come off quite arrogant. T2T constructively questioned your logic asking why would an oil change reset the ecu, and you reply, "No. There are no feedback sensors in the oil system other than the "idiot" light." Are you saying that no it wouldn't reset the ecu, which directly contradicts your first post, or are you making a completely irrelevant statement? Either way I don't understand the post. And then you add the extremely helpful statement "oil had nothing to do with it" as if you are offended that anyone might disagree or challenge your thinking. I'm not challenging your knowledge, as I know you're very helpful on the forums, but it seems awfully close minded to not consider all possibilities or let other people voice their ideas. I am not delusional, the odds indicate that the light will come back on, but I'm a positive thinker and I think I have described a scenario above that explains why I could be one lucky dude. If I am wrong please feel free to explain why.

[CDub]

ME- apparently the idiot lights aren't idiot-proof. In college I knew a girl with a jetta about 4 years old with ~60k on the clock that blew the engine. When she went into the dealer to have it checked they asked how often she changed the oil. She replied that she hadn't.......EVER! She didnt know what the light was so she ignored it and hadn't ever heard that you needed to change oil on a car. It's a good thing she is a very pretty girl.