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Discussion Starter · #1 ·
so on this 01 is300 my friend bought 1 cel code came up for bad o2 sensor, (bank 1, sensor 2), a week later, the auto parts store dumb-asses actually order the right one and we install it, i reset ecu, he drives it and all seems well, but that lucky little cel light came back on, now its reading 3 codes

1. P0420 (catalyst efficiency, bank 1)

2. P0430 (catalyst efficiency, bank 2)

3. P0420( catalyst efficiency, bank 1) PENDING

i know this has to do with the cats, so im thinking we replaced the right o2 sensor BUT now that its working properly its finding something wrong with cats? i guess...idk, any input is cool, oh and keep in mind when he bought this car, the performance was terrible, but it has aftermarket intake that looked like air filter hadnt been changed in 6 or 7 years (ridiculously dirty), so i replaced that and cleaned the maf that was hella caked with black grime and shazammm, power was back, so i think the maf couldve been dirty over an extended period of time making car to rich and possibly causing a problems that the cats are producing now......just what i think, but he doesnt want to drop the money on cats, and our state doesnt have emissions test so anything to get around these would be great????
 

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Discussion Starter · #2 ·
So guys, the only o2 sensor that was reading bad was replaced, but now that its coming up with the 2 separate codes for bank 1 and 2 catalyst efficiecy wouldn't that mean either both cats are bad or the engine itself is running rich, its getting around 18 miles to the gallon around town delivering pizza so this is why it really confuses me. So should I just get rid of the cats or what? And how could I go about just simply cutting them out?
 

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Sup man! glad to see you here!
is this your car or your friends' car???
Best thing to do is to just take it to a legit shop bro....sounds like there's major problems with the car.
Good luck!

V.
 

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Did you figure out the problem? I have the same codes.

Thanks.

So guys, the only o2 sensor that was reading bad was replaced, but now that its coming up with the 2 separate codes for bank 1 and 2 catalyst efficiecy wouldn't that mean either both cats are bad or the engine itself is running rich, its getting around 18 miles to the gallon around town delivering pizza so this is why it really confuses me. So should I just get rid of the cats or what? And how could I go about just simply cutting them out?
 

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2002 Lexus IS300 Sportcross. ~165K miles. (Bought from a board member in fact. )

Computer is telling me both primary cats are bad. Car drives fine and gas mileage is pretty close to advertised. I changed the downpipe gasket in hopes that an exhaust leak was causing a false secondary O2 sensor reading. No dice.

Is there anything else I can check before I shell out +$1000 for a new OE exhaust manifold?

I'd hate to spend $1000 only to find out I needed $400 worth of O2 sensors (4x$100). I'd also hate to spend $400 on sensors only to then need to replace the manifold as well.

Maybe it's worth forking over $100 to have a Lexus dealer diagnose it properly? Would they diagnose it properly or just tell me what I already know?

Well, sir, it appears that the computer is telling us your primary cats are bad. We can replace them for $3000 and we'll happily waive the $100 diagnostic fee.
 

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I had the same issue, got an O2 simulator and the problem went away.
 

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O2 Sim worked for me as well.


2002 Lexus IS300 Sportcross. ~165K miles. (Bought from a board member in fact. )

Computer is telling me both primary cats are bad. Car drives fine and gas mileage is pretty close to advertised. I changed the downpipe gasket in hopes that an exhaust leak was causing a false secondary O2 sensor reading. No dice.

Is there anything else I can check before I shell out +$1000 for a new OE exhaust manifold?

I'd hate to spend $1000 only to find out I needed $400 worth of O2 sensors (4x$100). I'd also hate to spend $400 on sensors only to then need to replace the manifold as well.

Maybe it's worth forking over $100 to have a Lexus dealer diagnose it properly? Would they diagnose it properly or just tell me what I already know?

Well, sir, it appears that the computer is telling us your primary cats are bad. We can replace them for $3000 and we'll happily waive the $100 diagnostic fee.
 

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You could always find a new manifold/cats from a car with less miles and save some cash that way. Considering it is throwing codes for multiple o2 sensors at one time sounds like you have a cat issue.
True but those codes also show if you're leaking between the header and the Y, doesn't always mean a bad cat.
 

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It would make sense that an O2 simulator would eliminate the cat code. However, that doesn't solve my problem unless the O2 sensors are actually the problem. If that's the case, I may as well buy new sensors.

I used a cheap IR thermometer this morning to test and compare the inlet and exhaust piping temperatures. If I'm not mistaken once the cat warms up it should operate and expel gases at temperatures higher than the inlet. After idling for 10 minutes the piping after the cats was still much colder than the piping in front of the cats. I was seeing inlet pipe temps of +400 and exhaust pipe temps <250.

Bad cats?
 

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I'm having a similar problem. I replaced an o2 that was bad, reset the car, drove it around, then got another CEL. Now I have 2 codes, p0057 & p0420. I just found out that the previous owner took out the cats in the car. Is there a way to make the codes go away? And what is an o2 sim, how does it work, how much does it cost, and can it take care f my problem? Any help will be greatly appreciated.
 

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I'm having a similar problem. I replaced an o2 that was bad, reset the car, drove it around, then got another CEL. Now I have 2 codes, p0057 & p0420. I just found out that the previous owner took out the cats in the car. Is there a way to make the codes go away? And what is an o2 sim, how does it work, how much does it cost, and can it take care f my problem? Any help will be greatly appreciated.
Here's everything you need to know, From where to get it and how to do it along with the cost. East simple fix, I'm going to be doing this also as i have the same codes because I have a aftermarket exhaust manifold, and GReddy exhaust.

DIY Thread
http://my.is/forums/f67/is300-how-i...ms/f67/is300-how-install-o2-simulator-342693/

Where to buy
http://www.o2simulator.com/index.php?main_page=product_info&products_id=10
 

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I took the car in for a "pre-inspection". Drove it cold from work. 2 miles. Tech said the car, "passes no problem".

So what does that mean? The tech's theory was that sometimes the car computer is more picky than the sniffer test. So if, for example, the cat is operating at 80% efficiency, the ECU might say it's bad, but the sniffer test says it's fine.

Plausible? Maybe the rear O2 sensors have drifted making the computer think the cats are bad?

Is it possible the front cats are still bad, but the rear cat, is doing all the work? It would seem to me that today's test would not have gotten the rear cat hot enough to do any meaningful work.

Seeing as it passes the sniffer test, maybe I'll just buy an O2 sensor simulator and be done with these shenanigans.
 

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Alright, got the car to pass. I still haven't solved the problem, but at least I'll get a damn sticker.

To pass, I cleared the code and drove the car 20 minutes from my house to the smog station. By that time, it had 1 readiness monitor that wasn't ready and 1 pending code (both for the cat). Neither will fail the inspection since the CEL wasn't on.
 
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