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Discussion Starter · #1 ·
About a year ago it came on with P0421. I decided to live with it and make sure I had the codes read and cleared every oil change. It has been the only code that sticks around.

I had my car jumped for the second time this winter (i'm told the battery is still charged though.. only a year old) and a couple of days afterward the light turned off while i was driving. It has been off for a few days now.

What's going on here? Is it the extreme cold messing with my computer? Was it the jumping that caused it? The first time I had it jumped it gave me a ton of codes, why would this one take them away? Was the original CEL not accurate?

If anything else, hopefully this post can be a light at the end of the tunnel for people with cat/o2 sensor code...
 

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2004 GLS 1.8T
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Shhh! Well, now that you've talked about it, it's probably too late. NEVER comment aloud when your car is running well!
 

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My CEL used to go out whenever the temps stayed above 60. I put the spacers on the rear sensors last year and the CEL has not come back on. Cheap and easy fix.
 

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Discussion Starter · #7 ·
nope everything has been the same except for the unusually cold weather (-10 instead of 10) and the jumping of the battery
 

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I'd suspect that when the battery died, it may have reset the readiness codes. If you have VAG-COM, you could check to see if it has reached readiness.

Our 2002 A6 3.0L Avant has has the P0421 code and once cleared, sometimes it can go almost a week before coming back, other times it shows up again much quicker. If all the readiness parameters are not being met, it's possible it could stay off for awhile.

Other factors could certainly be adding to the mix though, the temperature combined with the O2 sensor readings, etc..
 

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Discussion Starter · #12 ·
usually after i have the codes cleared i can get it to turn back on just by revving the engine pretty good. i haven't been successful in forcing it yet... i guess i'll keep my fingers crossed
 
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