Hello I need some advise what to do in this case.
I have recently replaced two new Denso o2 sensors bank 1 sensor 1 and Bank 2 sensor 1 because of an engine light indicator was giving me the following codes. 133-153. My car has about 47k miles and it was odd to me why my o2 sensors will go bad, but from a recent post i learned that they can go out regardles the milage. i went ahead and replace them and erase the codes with a code reader.
I had to get a Smog and it PASSED with great readings. but after about a month my engine light came on again and gave me the same codes I had before. I have already replaced them. I dont know what else can it be. plese help. i usually do my own repairs and had success till now.
Thanks.

What did you replace the 02 sensors with? I mean brand and type.

I replaced two brand new DENSO o2 sensors that I bought on ebay. they were universal in wich it can only be used before the CAT (Bank 1 sensor 1 and Bank 2 sensor 1). I changed the same wire color as explained on the box. four wire :black,black heater,and white and the other blue. I make sure they were the right color and came with the hardware that was easy to install. I dont know why i got the same codes but a month after p133 and p153.

Are you sure your wire connections haven't come loose? Even if you have to pull the connectors and just reconnect them and make sure. Then erase the codes and see if they come back. If they do come back again, then I would take the car in to if the sensors are bad. Maybe you got a defective sensor or sensors. I don't know how much you saved by getting them on Ebay, but if you go to Denso direct you can get them for 40(ish) bucks each.
Here's the link:Denso Website

I have already erased the codes. It lasted one day for the code to reapear and it came back few minutes right after i started the car, but this time only bank 2 sensor 1 was detected as low reading or code P153. weird only one code came this time i wonder. if the other one was bad it should have shown the code. I haven`t thought of taking it back out and recheck the plugs. I will try it and see if the code comes back again. I will look into the website u gave me. thank you for the advice.
im not looking forward taking the car to a mechanic, but i guess it may be something else wrong. You dont think is the kind of fuel im puting ARCO 91/premium?. I guess gas is gas but maybe is affecting the injectors from getting dirty.and maybe it was never the sensors in the firt place. I remember it lasted four months before the code appear again with the same codes.
Maybe I need to drive my car more ofter cause I only drive it about 15 miles or less a day.

It's possible your having an issue other than the o2 sensor, but seeing as how your here, you just as well make sure it's not the simple, cheap things first. If after your sure it's not the O2's and your connections, then maybe you won't have much of a choice. Have you cleaned the MAF, intake and throttle body recently? When was the last time you changed checked the spark plugs?

I have taken out the sensors and rechecked the connectors and plugs, everything seem ok and did not noticed nothing unusuall i make sure i erased the codes and i just have to wait and see.
Two months ago I purchsed a throttle body cleaner from a local Auto shop. I sprayed on the buttlerfly and clean it throught. Is that what u ment ? i have not taken the car to have it done at the shop the MAF seems clean. as far as the intake I curently have on a K&N typhoon cold air intake i also keep the air filter clean. Sparkplugs??? no i have not look into since it will be a process take them out as you already know. My car only have 45k miles. I know that they need to be replace every 60k.

Just so you know, I've heard alot of people have cel issues from the short ram/ cold air intakes. That could be your problem right there. If the cel comes back, you might want to think about putting the original air box back on and see if that cures the issue.

cel ???Yeah I suspected that this may be the problem, I thought K&N are good but I guess not on the IS. how does short ram/ cold air intake cel affect in this case. i wonder why. I dont really want to change back to the stock one. what would you recommend....
Am still sticking to the advice you gave me before, I have checked the sensors and seems ok. I will wait by changing gas stations brand like shell, Mobil, and 76, I have not seen any issues yet. I was thinking on maybe doing a different mod in the future withe engine, perhaphs, changing to an SRT intake but That will probably be in another department. Let me tell you I have seen how you are thrilled about cars, and how you have done it all by yourself by keaping youre rides nice, The Is 300 looks nice. I wish i can do that someday, hey am getting there. I have many friends that own the new gen, but not in black. Black is a nice looking color. my 03 is black but the sucker is hard to keep clean.

Thanks.

A "cel" is short for "Check Engine Light". The MAF on these cars are pretty sensitive. Alot of the short ram and cold air intakes seem to produce turbulant air intake. That and the fact the ECU's on Japanese cars don't adjust/compensate for the additional air intake ability like say a Ford. So really, I would just use the stock air box, and maybe a Joe Z pipe with a Blitz, K&N, or comparable drop in air filter. It would make your life a bit easier. The SRT does get you a few more pnies, but it uses a piggy back ECU that has to be wired in to your exsisting ECU, which is really where your getting the HP from. Unichip now makes an aftermarket piggyback chip that can get you about 12-15 more HP also, but they're $700.00 crazy!

Oh that`s what CEL means. I learn something new every day about cars.
Ive never heard of Joe Z pipe till today but it looks simple to put on and specially it gives out some more horses. I will look into that. I just hate letting go of the intake cause it makes a nice sound, I was actually thinking of doing a complete cold air intake or CCA so the filter would get better cold air. but oh well I had it for about Two 2 1/2 years. but at least I get to keep the high flow HKS exhaust pipe. Some day I will do a turbo but that would be a big project for me. I want to appreciate all your help.