jhip626

08 scion xb. after the exhaust rusted apart i had to replace the cat and everything behind it with aftermarket exhaust. Ever since then, i get an intermittent CEL and the code is p0420. if i disconnect the battery the light goes out for a few miles, then will come back on. and some times the light does go out by itself by just driving it..

i see alot of people get this code with installing headers and such. but this is just an aftermarket cat-back system... any ideas?

Tony31138

Did you install a stock replacement cat or an aftermarket "performance" one? Who did the work?

See this link to read about your code. http://www.p0420.com

The cel turns on when one of the continuously running self diagnostics tests fail. Disconnecting the battery resets the self tests from the beginning. It sometimes takes a little while for it to run through all the tests until it gets to the one that fails. That's when your light turns back on.

jhip626

its was an aftermarket oem replacement, not a performance one. I installed it myself. just a bolt-on. nothing too major.

Tony31138

Did you have the code before you started the work? Did you install new O2 sensors?
Keep in mind my mechanic cert level is strictly "shade tree."

jhip626

same 02 sensors... I got the code a month or so after installing the new exhaust... you and I share the same cert. I did body work for a living years ago... but this obviously isn't body work,lol

Tony31138

That's where I'd go with it. Change the O2 sensors, or just the downstream one. Mainly cause it'll be cheaper than another brand new cat, which might be the only other thing to cause that code.

jhip626

im currently trying the laquer thinner in the fuel tank, since that is the cheapest to try.... ill report back with results

Tony31138

Never heard of that. Let me know how that goes.

I thought for sure we'd get other people chiming in for this one.

jhip626

did the "ONE GALLON OF LAQUER IN A 1/2 FUEL TANK" The light didn't come back on until 20-50 miles or so after my wife refilled the fuel tank. so I don't know if that actually did anything or not.

RichBinAZ

Thanks for letting us know the "thinner" didn't work. I can safely place that with all the other fuel additives now in the "does not work" column.

Changing the O2 sensors seems sensible to me. They don't last forever

jhip626

a lot of people swear by it, I may even try it again, just to see if it helps anymore. but a lot of what im reading says it could just be that Cat. so idk.... Im afraid this will just end up me replacing the sensors and cat in the end.

Tony31138

If you reset your cel when you put the snake oil in, 50 miles is probably the length of time it took your car to run through the self tests. Or did the thinner cause your light to extinguish? I'm just curious.

jhip626

Has anyone tried the spark plug fouler trick with this car? not sure if It would work or not.... my biggest complaint with this is when the CEL goes on, the traction control and abs lights go on too... its like wtf?! why?!