heatsoakedS4

So I've had the all too common and ever ubiquitous 16805/16815 Cat warm-up code pinging my CEL for YEARS. Despite all my attempts at a fix, it returns within an hour of clearing them. I've simply learned to live with it.

However, that was until I changed my fuel filter. Lo and fricken behold, for the first time since 03, NO CAT CODE! Now after STFA'ing, changing the fuel filter has NEVER come up as a means to reconcile this code. I DIY but I'm no mechanic by any means but it doesn't make any sense to me how putting in a fresh fuel filter will clear this code! Am I missing something? Is it a simple coincidence?

kelbrig1

Did you disconnect the battery when you changed the fuel filter?

heatsoakedS4

Nope. Just pulled the fuel pump fuse and cranked it.

kelbrig1

Hmm, I'm assuming it's been off for over an hour now? Nice job. Let us know if it returns

heatsoakedS4

Over a hundred miles and nuthin.

-SlowSilverTIPJason-

maybe it was running lean during a cold start when its in open loop. I guess that could result in higher NOx and could render the cats less effective.

UberVier

I almost guarantee you within 5K miles it comes back.

I swapped my fuel filter out at 60k miles, and was floored with how different the car idled and ran. Amazing difference. At 72K now, I can feel the misfires and stumbles again. Once in a while I would get the misfire codes before I changed the filter. Those codes haven't come back, but I'm sure they will at some point.

Hell, change the fuel filter every 10K miles.

heatsoakedS4

Never checked. Good theory.