Catalytic converter issue??

[Legy2000]

So, my 2000 GT keeps throwing code p0420 at freeway speeds. I reset it and it comes back. Usually around 70mph. 

My question is....

Should I replace the catalytic converter or the O2 sensors??

Any and all input is appreciated 

 

[doublechaz]

Miles on the cats?

Miles on the O2 sensors?

Can you get your hands on a live data scanner?

What other history can you give?

It would be best to have the scanner and look at what the O2 sensors are reading.  In today's market where it can be difficult to get good parts you don't want to swap for new junk sensors unless you are sure the old ones are done.  In the old days I would replace them with much less scrutiny.

 

My cats were doing fine at 250,000 miles, but I always kept it well tuned.  At that point I had a problem that took a bit to figure out and in that time the cats carboned up real bad so I replaced them with magnaflow direct fit.  I've been happy, but that was so long ago I don't know if those are still available and good.

If your car has gone long periods with small fueling problems then your cats may die long before 250k.  I also don't know how long they can go without the problem I had.  But at some point they typically have eroded away enough of the platinum and palladium that they just don't do their job and you get that p0420 code even when the second O2 is still good.

 

[Legy2000]

Car has 225000 on it. Just got it, don't know history. 

I don't have access to live data. Only a cheapo data link via bt. It only shows 1 o2 sensor activity. Not both. 

I did see that the magnaflow setup was available. But that's booboo $$$$. 

 

[doublechaz]

Yeah, I think it was close to $600 for the pair of cats when I did it way back.  Must be crazy by now.

At 225k the cats could be used up, or not.  Can't really tell for sure.  How does the exhaust smell?  Mine doesn't smell bad at all with it working, and it stank of petro-chemical-yuck when it was broken.  Not really gas smell because the gas is mostly burned.  Kinda a mix of gas and varnish and maybe some kind of burnt food or something all mixed together.  If you know, you know.  If not...  If it really smells yuck and the engine is running healthy otherwise that might make me lean just a tiny bit toward cats being done, but again, I wouldn't sign my name to it.

Do you know someone with a scanner?  If you are in sorta central Arizona we could meet up for a scan, but that would be uncommon luck.

There is the multimeter way to probe the O2 sensor voltages manually, but that is a bit more advanced of a technique.  Not rocket surgery, but not as easy as reading a scanner graph for a minute.

[Legy2000]

Ya, the exhaust does smell a little off. I may just pull the trigger on the cats setup. 

Im experienced enough that I could probably do the multimeter thing. I just don't remember which wires to check.

[doublechaz]

That is what the book is for. 

[Legy2000]

Don't have one. LOL. yet. 

[doublechaz]

I didn't go on "vacation" every year that Subaru made cars, but many of the years.  Search for "vacation pics" on this site and see if you can see anything useful.  There are a lot of dead links in that thread, but persistence usually pays off.