P0420 question

[TheGreenDutch]

I had a shop across the street from where I work do a tuneup and valve cover job. My 2000 v6 Cali spec had a little cold start bucking back when it was cold that would go away when warm, but no cel. So I get my car back and the guy who did it said oh the cel came on and he cleared it but it should be fine. The code is the cat below threshold SOB. I don't know what these idiots did, but now I have to deal with this. Of course they're acting like whatever and I can't let anything escalate because of the situation I'm in. Is there any wires or anything that he could have pulled out to get to the valve covers or vacuum hose displaced I could look for? I went to the camrystuff.com site and looked at the manual.Everything looks normal. The car runs great since I seafoamed it and did the MAF cleaning and Coilpack dielectric grease cleaning. I changed the a/f sensor in front even tho when I tested the old it still was within spec. Is that one at the firewall maybe the culprit before I have to buy a new cat? Could I use the old one in the back to try out. I found a source saying its the same just the wire is longer or shorter?...bah...please help. My lara only has 139 grand on the ticker.

[TheGreenDutch]

Light went out while purchasing a bacon,egg and cheese biscuit. Maybe cleaning the MAF, IAC, Throttle plate did the trick and the computer had to relearn itself after the valve job. Clearing the code did not let the hard save erase I guess? Anyway she runs great. I swear in the past month I've read every p0420 code forum question on the net....lol

[Jason.MZW20]

Well for future reference, the ECU compares the upstream O2/AFR sensors output to the downstream O2 sensor output. Usually, the downstream (after cat) O2 sensor sees a relatively constant output. Once it starts varying its output, the ECU will throw a cat efficiency code or a B1S2 O2 sensor code depending on the issue. Though, I'm sure you read all of that somewhere.

If you have an A/T CA spec 1MZ, then you also have warmup catalysts on each bank (M/T don't). This will help the main cat do its job and a cat efficiency code will be less likely (not impossible) unless you have a significant air-fuel ratio imbalance that damages the catalysts.

Glad everything worked out in the end.

[TheGreenDutch]

code came back today....Looks like I'm have to get dirty.....and thanks Jason for the info....