2002 Outback code PO420 back again

[ursina]

My 2002 4 cylinder OB kicked out the PO420 code about a year ago. The dealer said there was an exhaust leak in my down pipe (y pipe), so that pipe was replaced. Car ran great with no code for 6 months, then it kicked out the PO420 again. So I replaced O2 sensor in Bank 1, the front cat. All is great for six months.
Now, I had my 90k service last week (not at dealer), where they did all of the fluids and plugs (some make and model plugs), but no the fuel or air filters replaced. Yesterday, I drove a couple hundred miles with a lot of stop and go and the check engine like came on, then went off for about 20 miles. and then came back on. I went to the parts store today and they said that it was code PO420. This is driving me nuts!

I have googled this code and it seems like it is a curse the OB to kick out this code and I have no idea what to do now. I have a road trip this up coming weekend Memorial Day weekend where I'll be doing well over 1k miles with a lot of stop and go. Should I try to fix it before the tip or figure it is a false code and have it check out when I am not in a rush?

Thanks in advance!

[bertmaster2000]

ursina,

you might notice on this blog i am having a similar problem with my 1997 outback with a 2.5l 4 cyl automatic. since i replaced both front and rear o2 sensors in my car within the last about 10K miles, and the fuel and air filter within the last 100 miles, i have not experienced any hesitation on acceleration, so i am confident the minor exhaust leak i have at the manifold is the reason why my check engine light turns on some days and is off other days. my car even passed emissions testing last month, so i know my check engine light problem is not significant!

since you will be driving 1K miles this coming weekend, if the check engine light concerns you i have found one way to cure it (for awhile anyway) is to add one bottle of high quality fuel injector cleaner and one bottle of high quality octane booster to one tank of gasoline. i would bet the check engine light on your car turns off after you drive 50 highway miles because these 2 additives combined with high rpm driving will clean your o2 sensors to some extent.

in your case, i would drive your car without a worry until there is a real symptom such as hesitation on acceleration or poor idle. the problem your car is having will not leave you stranded, so drive it until the problem becomes 100% diagnosable with both engine code and a symptom (or symptoms) that can be felt/heard/etc.

good luck and drive worry-free this weekend!