2002 Pontiac Montana Error code P0420

I failed my emissions test the other day, the service engine soon light was on, got an error code for the o2 sensor (P0135) and also had a thing on there that said incomplete oxygen and catalyst monitors. So, later that day I got an o2 sensor from Napa, headed to my cousin's and replaced it. It was the upstream which is located on the exhaust manifold (which was hell to replace). The SES light was off at that point, so I breathed a sigh of relief and headed home, which was an hour away. About 35 minutes later the light came back on. Today, I went to both autozone and advance and did the diagnostic test. No code for the o2 sensor, but now I've got error code P0425 which says "catalyst efficiency below threshold." The guy at autozone said I just need to drive it a certain way to reset the cat monitor, and the guy at advance said I need a new cat. The car runs just fine, no problems whatsoever, and I just need to get this thru the emission test so my plate doesn't lapse. Can anybody give me any advice as to what I need to do and how to do as inexpensive as possible? If I need a new cat, that's fine I'll do that, but are there any quick fixes to get me past the emissions test for now? I just can't afford to have it fixed right now and I'm on a time crunch.

The catalyst code is pretty straight foreward, you need a cat. You can try clearing it and hope it does not reset, other than that, you need to replace the converter.

how do you clear it out?

What did you do to clear it out?

I haven't done anything yet. I don't know how to clear it out

So can anybody tell me how to clear out my catalytic converter? Also, would I be able to squeak by the emissions test if I had the check engine light turned off right before I went to the test site? One last question, has anybody ever heard of or have experience using the CRC Guaranteed to Pass Emissions Test Formula? Here's a link from Amazon:
http://www.amazon.com/CRC-05063-Guaranteed-Emissions-Formula/dp/B000CIPUR8

Apparently they sell this at Advance as well. Never heard of it until yesterday. Can anybody provide feedback? Will this be an effective bandaid for me to get thru the emissions test? I appreciate all help and advice

You might use a H20 cheater down stream until a new catalytic converter @
www.catalyticconverterwarehouse.com

all I saw on that website were cats. What's an h2o cheater?

Do a Google ''H20 cheater spark plug non fouler''

Don't forget to clean all the cat guts down stream of the exhaust system.

When I said to clear it, I meant clear the code. Would need a scanner to do that.

oh ok, I'll take it to autozone and see if they can clear it for me.

You not only have to clear the codes but all the readiness "flags" have to run and pass...if they don't you won't get a sticker...

As for the P0420, the usual culprit is the cat.....however proper testing should be done......it could be the rear O2 sensor, the wiring to it, or a PCM problem, also.....

Usually, you graph the front and rear O2 sensors...if the graphs are mirror images of each other, then the cat is no good....

Is there a proper way to clear the cat guts down stream of the exhaust?

Not sure what you mean? Are you thinking the exhaust is blocked after the cat, after replacing the cat?

Not sure what you mean? Are you thinking the exhaust is blocked after the cat, after replacing the cat?

Do a Google ''H20 cheater spark plug non fouler''

Don't forget to clean all the cat guts down stream of the exhaust system (http://www.automotiveforums.com/vbulletin/#).

that was said a few replies ago. that's what I was referring to, whether or not I could clear the cat out and get the light to go off

If the catalytic converter is blown (P0420), broken pieces from the cat could
block exhaust flow.
A plugged catalytic converter could lead up to random misfires, damage heads, and head gaskets. There is no Diagnostic Trouble Code ''Catalytic converter Blocked''

Have a local muffler shop check both cats + exhaust system out, also have new rubber muffler hangers installed.

Yes - You could clear the Check Engine Light (CEL), it still will throw another code, and the inspector will know because the drive cycle is ''inc''

oh ok, I'll take it to autozone and see if they can clear it for me.
I find that when you clear codes, you wind up being in the dark about your engine's status, wondering if the light will come back on. You can't take it to get tested unless you are sure the monitors are ok. This requires a scanner. So, by leaving the code there, when the light goes out, the problem is gone and you can get it tested right away.

My wife's van gets the same code when she drives small distances around town. But if she goes out on the expressway and cruises for an hour, the light goes out. So we know to do this prior to a test.