changed O2 sensor and cat, but still have P0133,P0420,P0440

Well, the 440 and 442 are unrelated to the others. They're EVAP and let's set them aside for a minute. You replaced the O2 sensor, but the light was still on and the codes were still there because you didn't clear the codes. Secondly you never replaced the catalyst. Both P0133 and P0130 would indicate most likely a bad o2 sensor, although a wiring issue isn't impossible. So replace both sensors and the cat and clear the codes. See if your 0133 0130 and 420 go away and if they do, they we can tackle the EVAP codes

helo !

I agree a little with Darkrooms. First, before attemping to change the converter, you should try to check if there is no exhaust leak near the converter and near the exhaust manifold or pipe.
If you already change the O2 sensor ( you told us you already did it ) there could be another problem like the one I´m telling you.
Because the first oxygen sensor is reading bad then the 2 second one (the one after cat) could be false compared with the first one (because of the computer false reading signal).
The other posibility is that if you have some exhaust leak, the converter could not be reading OK.

Keep posted

it took 2 days because of how many trips it takes for the monitor to complete! replacing the 02s did nothing! you don't know how to check for an exhaust leak? how did you manazgae to diag the 02 then?

Look, your MIL keeps coming on because you have EVAP codes recurring at different times. They're not going to go away. Even if you fix the Cat the o2s successfully, your MIL will still illuminate because you have EVAP issues. It's gonna take time, $, and patience to get them all. Catalyst codes, in my experience aren't caused by exhaust leaks. The reason is that exaust leaks cause the post o2 sensor to go static or quit switching or to switch at a different threshold. A bad cat causes the o2 sensor(post) to switch very rapidly, matching the pre sensor. Just trust me, 99 times out of a hndred, catalyst codes = bad catalyst.

This is a great site for auto repairs advice. My '02 Camry has a Check Engine light and I had it checked at AutoZone and code P0420 came up. My suspicion is that my engine seems to make a howling noise when it is running. I can't pinpoint exactly where it's coming from, but it seems to be coming from the top of the engine somewhere. Could this howling noise be the culprit (vacuum leak)?

no it's probably the converter

If the tailpipe has plenty of air coming out, is it an indication that it's not clogged? I guess I just don't understand how the cat converter works. If it is clogged, no air should come out at the tailpipe.

Change the CAT ¡
Inspect the pipe near the cat, the sound you are hearing could be the broken catalystic, you must replace it to fix the code.

Also, what happened with the O2 codes ?
Did they reappeard ?
Did you cleared the codes ?

Keep posted

OP: you won't be able to detect a catalytic converter problem by feeling for airflow out the tailpipe. Often they are trash and not because of being clogged, but rather the catalyst isn't working anymore. Replace it.

Here is something very odd that just happened right after I changed the oil. While changing oil, I also was checking for any leakage (vacuum lines, cracks, gaps, etc...) Didn't see anything out of place. I disconnected the negative battery cable so it reseted my code. After I connected everything back on, I started the car and it acted like it didn't want to start. It started but die right away if I let go off the gas pedal. It ran with really low RPM (250-500 RPM) so the engine was shaking like crazy. I turned it off and start checking for something I may have accidently unplugged. Nothing unusual found. So, I let it sit overnight and it started fine in the morning no sign of the day before. I drove it to work and within 35 miles or so, Check Engine light back on. Haven't have it checked again, but I assume it's the same code. Would a bad O2 sensor turns on the Check Engine light right away? Or would it take longer for the light to come on? What about the cat converter? I guess with a good mechanic, he/she may be able to tell which one is the culprit by looking at how fast or slow the Check Engine lights comes on. But I'm not a good mechanic, so I can't really tell. Any lead?

Helo

You must replace the cat..
What I´m thinking, is that you are wanting to know, what faulty is the responsable for turning on the check engine light. Because you only want to fix one thing to easily turn off the light.. ( I guess , Im OK ?)
OK... you have 3 different failure codes, each one is individual and they reffer for 3 different failures they have to be resolved separately.
If you think, repairing one failure (like o2 sensor ) it will put out the check light,, these would never hapen. Eventhough you want to know whether the O2 sensor or Cat were the responsables for turning on the light, you will have to fix the other failures. If it is remainning one failure to be resolved (for example the EVAP code ) even the cat or O2 sensor are replaced... believe me,, your check light will be there.. until you fix the other different problems..
So a good way to start is to change that CAT, and after that you can focus on the EVAP..
Also, if you want to know what code is first displayed... you can buy a code reader (they are nice and cheap)

Keep posted

I'm waiting for my Stimulus check from IRS. When I receive it, I will buy an Actron CP9190 Elite scanner, which would be more sophisicated (than a basic reader/scanner) to help me further isolate the problemed components. And you are correct, I'm only interest in fixing the exact problem as I try to minimize the cost as much as possible. I do not have any other code but P0420. So I'm not sure if EVAP also plays a part or not. How much is a typical catalyst converter?

Helo
Definetely,, the EVAP plays part on the codes,... The reason you don´t have now the EVAP code is because: To register the EVAP code, it takes more time (trips) to register it it. But as long you don´t resolve the EVAP you will get the code..

couple of things 1 sometimes after market o2 sensors have a wider parameter then the original equipment. i do alot of work for a toyota dealer and ran into this problem before. also they make 2 different converters, regular obd2 ready and obd 2 cat this one is bigger and has more area. any cars after 2000 usaully need the larger of the 2. hope it helps