another 2k camry cat question

so. I have a Japanese 2k Camry
I've been to 3 autoshops.
tiresplus was thinking that it was the front cat.
the other 2 weren't sure from pulling code which at was the problem, but they were sure the o2 sensors weren't the issue.
i just replaced my front cat.
(ironically from a shop that I didn't ask them to pull the code, i should've)
after replacing my front cat (imo its not blowing as much smoke out of the back), but the engine light came right back on.

So... I am left with the conclusion it is the rear cat. Can I get away with just putting a universal cat on the back of the car, or do I have to get another expensive part.

Any and all advice would help. I've already blown significant money on this.

What code(s) did your ECM store?

The code is important...a bad upstream O2 sensor can ruin a cat.

p0420 finally was able to pull it. catalytic efficiency below threshold.

So far the work on my car is.
1. oil leak in the gasket - so i replaced the spark plugs and the seals around the gasket. the mechanic said regular spark plugs were good enough so thats what i put in them.
2. replaced the front CAT

i am going from memory here. but the mechanic at the autoshop said it didnt' matter if i didnt' install the recommended spark plugs (which seemed to be of higher quality , definitely higher price), but that regular spark plugs would work just fine. Very soon after he installed new spark plugs and gaskets i started getting the catalytic inefficiency issue. could the spark plugs be the problem?
-Luke

Toyotas don't seem to like plug brands other than DENSO or NGK. Only use those.

The ECM compares the waveform of the HO2 sensor located before the cat converter with that of the sensor after the cat converter. If the waveforms have the same amplitude, then the ECM sends out a DTC0420 code. The possible problems (which may have been caused by your plugs if they misfired alot) are in the HO2 sensor or the cat converter. It may also be an open or shorted sensor circuit, which would not possibly be caused by your plugs.

i had placed in my car were ngk single platinum plugs instead of the double tip (at the recommendation of the mechanic) the double tip plug is the recommended plug.
so are you saying that could be the issue?
btw I bought my toyota at 355 toyota. hehe

Use identical (or nearly so) plugs as originally installed, including electrode configuration. It is unusual for plugs to cause this DTC, but not impossible. Most likely, your HO2 sensor is bad or your wiring harness to the sensor was damaged. I think a problem with the cat converter is the least likely of the possible causes for that DTC.

I have had reasonably good luck with 355 Toyota maintenance and their parts department is really knowledgable and helpful.

A bit more info: http://www.obd-codes.com/p0420

unfortunately i'm not near the pike these days but am in KC. thanks for the tip. I called the mechanic where i had the plugs replaced and he said he would do (labor wise) for free and i pay for parts. Nice guy. I wouldn't think its the plugs either except, that this problem started only a few weeks after i had the work done there.