So I just got my 02 LS430 very recently, and just the other day a CEL popped up.

I got it scanned and it ended up being P0430 which is "catalyst efficiency below threshold (bank 2)". My question is, how can I figure out which O2 is bad? If it's even a O2? Is there any way I can CONFIRM what's wrong before I spend money on the wrong part? I didn't notice or hear any exhaust leaks, so I don't think its a leak. Car is at 94k miles if that matters. Thanks guys

 

Based on my experience with 2 different LS400s, when an O2 sensor goes out, the code reflects exactly which sensor -- both of my cars needed a front driver side O2. It's not hard to change if you have the proper socket, extensions, and hopefully an impact gun to break it loose.

From your code, it's not evident which O2 is bad, if any. More research needed?

 

Online it just says either O2 or Cat bank 2. That doesn't narrow it down too much

 

You will not find an exact diagnosis for this code. A shop will tell you to replace the cat. It could simply be that carbon build up needs cleaned off. Run a fuel and exhaust cleaner through for a tank and reset your code for the next tank. It may solve the issue. If not, you have some troublesome money to be spent - could be plugs, could be O2 sensors (both pre and post cat) and lastly, could be the cat itself. But hopefully the exhaust cleaner burns off the deposits and prevents code from coming back for the cheapest solution.

 

Here's the troubleshooting procedure for P0420 (Bank 1) and P0430 (Bank 2).

 

Ahh the old 420 and 430. I had to deal with this with my LS400. The previous owner was resetting the code and it would take about a week to pop up.

In my case it turned out to be the cats. I replaced both post cat O2 sensors as failing cats are very rare but I do believe if the previous owner ran 87 octane the majority of the life of the car this will ruin the converters. It was not the sensors. Double check for leaks as well. You may need to rev the engine up around 2000 rpms and have someone under the vehicle to detect small exhaust leaks.

If it is the cats make sure you get the kind that rated for this car. The 400 and 430 are sensitive and they need a cat with higher content of precious metals. OEM cats are out of control expensive. I think mine came from Magnaflow and were around $500 for the pair vs $1200 each for OEM.

 

Clear the code and see if comes back. If not don't worry about it. It happens every so often to me, but it hasn't come back for 8 months or so.

If it keeps coming back, check for a hole in the y-pipe of the exhaust. It is a relatively common problem. I believe you must remove a heat shield.

If not it's the cat, which should be replaced. Obviously aftermarket is cheaper. The Magnaflows as some have recommended should do the trick.

 

How many miles on the clock? As is often the case, pre-cat O2 sensors aren't replaced under routine maintenance and the cat ends up being destroyed. If it were me, I'd do the testing supplied by rkw (post 5). But since you just bought the car, I'd replace both pre-cat O2 sensors especially if you do need to replace any cat. Otherwise, you may replace the cat which is only fixing the symptom, and not the cause of the problem - a faulty or marginal O2 sensor - only to have the new cat get destroyed due to a malfunctioning O2 sensor.

 

OP has another thread where I asked same question of miles on the clock. 92k

https://www.clublexus.com/forums/ls-...iful-02-a.html

 

Quality of gas is important also.. had the code pop up on my 4Runner, could clear it and run Texaco/shell/exxon and not have a problem. First tank of QT or racetrack and the code would come back. Just my experience...