smokey25

Yay, i have had an on again off again.. well mostly on CEL for the past 3 or 4 weeks in my 2000 2.5RS. I had the code pulled, it is a P0420 which is "Catalytic efficiency below threshold" or something close to that. Now here is some backstory..

About 5 weeks ago my car blew its headgasket. I'm pretty confident i caught it the day it happened, i was dropping my girlfriend off at the airport and on the way back the engine was getting a little hot. I was about to take it to the shop when i checked my oil before i went and it was full of milky sludge. So i take it in right away, they change the gasket, timing belt, water pump, pulleys and a whole bunch of other crap. I get the car back and it runs great. I had a small crack in the exhaust header on the driver side right after the bend coming from the engine. The shop also welded that up for me and the car sounded great, they did remove the heat shield from that part of the exhaust. Thats all the crap that happened to my car before the CEL.

So a week after that the CEL pops up. I really want to know what i have to fix to get rid of it. Some people think its the GAS CAP, and once the CEL did go away after tightening it. I even bought a new gas cap, but the CEL is still on. Some people think its an 02 sensor going bad, and they say that the burnt coolant from the blown gasket could of caused that. The only thing i don't want it to be, cause it is the most expensive is the actual catalytic converter, but could the cat be bad on a 7 year old car? Would the burning of coolant make the cat go bad like that?

Anyways, i know you guys are smart so if you know what my problem is or have any ideas or experience let me know

Roo

iTrader: (3)

Coolant is bad for cats of any variety...both feline and the converters that live in your exhaust system.

Coolant is potentially deadly for both.

Check your mileage. If it's below a certain amount (IIRC, 70k), you might be able to get it under federal emissions warranty.

WREXNFX

iTrader: (3)

there is a few ways to test this one is to drive the car really hard
if it starts to misfire under heavy load your cat is restricted or have a shop put a back pressure guage in the o2 hole and check the back pressure before the cat and see if its too high which would also mean a restricted cat
you will also feel a lack of power
more then likely it just clogged the rear o2 sensor and should replace that o2

smokey25

Thanks guys.

The car runs awesome. I've ran it hard at high RPMs and there is no hiccup at all. This is such a pain in the ***.. what would you guys recommend, replacing the cat or the 02 sensor? I'm thinking its the stupid cat.. ****!

Could you go get a used catalytic converter from a pick-a-part place?

WREXNFX

iTrader: (3)

why dont you ask to borrow a cat from someone on here that is running catless and has the stock on layin around see if that fixes your problem if it doesnt then its the o2 sensor

smokey25

I would, but i'm out of town.. but i asked some people up here too

scarface

iTrader: (3)

what up smokey!!!!!! crazy problems your havin. You should call Andrew at S and S in concord see what he thinks.

How things in BC bro? You gonna be up there for good or you comin back to cali???

Later, good luck with your problem.

Hoofus

I'm having this issue. I originally had a code for the front o2 sensor and replaced it. Now the code is for the catalytic converter. Should I replace the rear 02 sensor or?

I have no hiccups at higher RPM's and power seems just fine. I'm running at 148k miles.

slugrx

iTrader: (12)

My friend had a 08 2.5i and his car had the same cel and it was a clogged catalytic converter, luckily he was 500 or so miles before his warranty expired so he got it done for free

Replaced the cat and no more cel

eastbaysubaru

iTrader: (9)

I've got the same code and haven't spent much time looking into it because the car is running fine. FWIW, you should probably check out rs25.com if you haven't already as there's quite a bit more info over there vs. an i-Club.com regional forum. Good luck and let me know what worked for you so I can do the same

-Brian

Hoofus

hah well I wanted a replacement for Nasioc that's why I came here. Much more accommodating to newbs . I think seeings how its running just fine I'll leave it be. It comes on about 1x a month or so and I don't have any misfire codes nor any hesitation.

Might just beat the cat material out and run a straight pipe IF or WHEN it does back up and cause a backpressure issue. I have other plans for my 280$.

GD916

iTrader: (2)

2 weeks ago I pulled a PO420 on an 03 corolla, I replaced the cat, and it hasn't come back on me yet.

Hoofus

Is a cat really required in our cars, or does the first 02 sensor control the F\A ratio.
IE: Will anything bad happen if I run without a cat?

MarvZz

iTrader: (8)

A shop should be able to check the o2 sensors to make sure they are functioning properly. Or if you know someone with a good digital volt ohm meter you can check it yourself by using t pins in the back of the sensor with the car running. Voltage should fluctuate slightly. It is possible that the cat is bad from the coolant.

GD916

iTrader: (2)

YES! not that it matters, but its usually referred to as "a/f" ratio.