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Yeah, the Lexus Global Service Information Center software that I have has a troubleshooting section for all codes and for and P0430, these are the four culprits. Unfortunately, I can't share/link the whole section here so I'll just list the trouble areas they want the technician to look at. Bank 2 is cylinder's 2, 4 and 6. Sensor 1 is upstream and sensor 2 is downstream.
1. Gas leakage from exhaust system
2. A/F sensor (bank 2 sensor 1)
3. HO2 sensor (bank 2 sensor 2)
4. Three-Way Catalytic Converter (TWC) (Exhaust manifold)
Many people go right to the TWC since that what the code says. I hate to replace parts/sensors that I don't know have failed, but sometimes it's cheaper to just replace it, especially on a 13 y/o car that you may not have the entire history on. As you are finding, Lexus cats are hard to find and not cheap. Aftermarket cats are hit and miss.
It still may be your TWC, but I'd eliminate exhaust leaks and sensors 1st. Also double check electrical connections to the sensors. Clean and re-snap if possible.
Yeah, the Lexus Global Service Information Center software that I have has a troubleshooting section for all codes and for and P0430, these are the four culprits. Unfortunately, I can't share/link the whole section here so I'll just list the trouble areas they want the technician to look at. Bank 2 is cylinder's 2, 4 and 6. Sensor 1 is upstream and sensor 2 is downstream.
1. Gas leakage from exhaust system
2. A/F sensor (bank 2 sensor 1)
3. HO2 sensor (bank 2 sensor 2)
4. Three-Way Catalytic Converter (TWC) (Exhaust manifold)
Many people go right to the TWC since that what the code says. I hate to replace parts/sensors that I don't know have failed, but sometimes it's cheaper to just replace it, especially on a 13 y/o car that you may not have the entire history on. As you are finding, Lexus cats are hard to find and not cheap. Aftermarket cats are hit and miss.
It still may be your TWC, but I'd eliminate exhaust leaks and sensors 1st. Also double check electrical connections to the sensors. Clean and re-snap if possible.
Good luck.
Interesting, I would've never thought that an upstream O2 sensor would have any effect. But I suppose it makes sense if one is giving the wrong readings to the ECM and it's screwing up the fuel mixtures on that bank or something. OEM units are $125+ on RockAuto so I think I'll try switching both sides first before spending that cash.
I'll check the exhaust again but I'm confident there's absolutely no leaks leading up to the downstream sensors. You don't think that a leak AFTER the downstream sensor could trigger a code, do you? I ask because I've had sections of the midpipe cut and welded in last year, about 2-3 inches PAST the downstream sensors. I don't recall seeing those new sections/welds leaking at all but I guess it couldn't hurt to triple check.
I'm not an expert, but I'd absolutely check the midpipe section that was cut and welded for possible leaks. Depending on the size of the leak (potential) 2 to 3 inches past the sensor could affect a reading.
I believe the advice ibidu1 shared concerning plugging the tailpipes to check for leaks is still valid. Maybe there was a weld that cracked due to driving, or maybe never done properly. Compare the welds for both passenger and driver's side since it appears you have no issues with bank 1.
I'd focus on the midpipe prior to swapping out upstream sensors.
Majority of the the bad cats on here are from leaking pipes. Im not saying they go bad, but lexus has durable quality then say Ford. If you cant find any leaks, I would take it to a good mechanic that has a good scan tool that can monitor and compare the o2 sensors as they heat up. I would avoid buying parts in hope for a fix, take it to a good quality mechanic that will properly diagnose
Majority of the the bad cats on here are from leaking pipes. Im not saying they go bad, but lexus has durable quality then say Ford. If you cant find any leaks, I would take it to a good mechanic that has a good scan tool that can monitor and compare the o2 sensors as they heat up. I would avoid buying parts in hope for a fix, take it to a good quality mechanic that will properly diagnose
I would absolutely put more trust into a Lexus than a Ford, but no car is perfect. A scan tool like that would be ideal, I'll see if I can get my hands on one.
I'm also tempted to try 1 more bottle of CataClean, I could've sworn I've noticed a difference the first time around.
I've read about that tin covering on the AWD midpipes... my car doesn't have that. I think they tweaked the design of the exhaust for the 2009+ MY cars. I've inspected the exhaust several times myself and had 2 shops look as well, a tiny leak was found in the flange about 8 inches in front of the downstream o2 sensor, but it has been since fixed and the code still returned.
I can check the temp like you mentioned but vehicle performance is just fine with no bogging or anything suggesting a clogged cat.
However I would have to disagree with you in terms of failure rate.... cat failures seems to be a common issue on these cars, a search on this forum and other Lexus groups will reveal a lot of P0420/P0430 issues. I've owned this car since December 2020 and never had any issues with misfiring; perhaps the previous owner neglected it at one point but not while it was in my ownership. It is worth pointing out that my car consumes some oil as well (about 1 quart every 3k miles) so that may have fouled them.
I just checked on youtube and the video on how to replace transmission fluid on a 2011 gs350. It does have the tin covering on the mid pipes. Maybe you purchased your car used and the previous owner removed them. But if they are still there, I would suggest you completely remove them to fully inspect the tubes. Also having someone seal off the exhaust tips will help you reveal any leaks. I would repair any and all leaks, as a small leak can throw off the o2 sensor readings
I believe everyone is offering advice to help you resolve your issue, without going the most expensive route. P0420/P0430 codes are common, but my experience is that the cat is the most expensive fix and only one of many things to throw the code. I've had P0420 and P0430 codes. My fix was replacing the rear O2 sensor, a spark plug change, and injector cleaner with known premium gas. You've done due diligence replacing the rear O2 sensor and chasing down at least 1 exhaust leak. I think it's prudent to also check/replace the upstream O2 sensor and absolutely block off the tailpipes to confirm absolutely no leaks. If you've convinced yourself all else is fine, then replacing the cat is the thing to do.
When the rear O2 sensor was replaced, did you use a genuine Lexus O2 sensor or a genuine Denso equivalent?
Also, if you are burning 1 qt of oil every 3k miles, you may have carbon build up on rings/valves in that bank. It's possible the front O2 sensor has seen more unburnt fuel/oil than designed so the ECM check between front and rear O2 readings is throwing the code.
If it runs well, great, but have you considered pulling the plugs from cylinder's 2,4 & 6 and reviewing?
Good luck.
So I pulled the 3 plugs from bank 2 and 1 from bank 1 (only did cyl 1, was running out of daylight and I didn't feel like removing the intake for 3 and 5 lol). Here's how they look after about 20k miles:
cylinder 2 ^
cylinder 4 ^
cylinder 6 ^
cylinder 1 ^
cylinder 1 and 6 plugs next to eachother. #1 is on the left ^
Last edited by artfil91; Jun 24, 2022 at 08:06 AM.
What are your thoughts for these plugs with 20k miles? Definitely signs of oil consumption on bank 2 (with #6 appearing the worst), bank 1 doesn't seem awful with a little oil burning (but granted, I only pulled cylinder #1).
I've changed the plugs on my car 3 times over the years, it's easy, never had to remove the upper intake manifold like on some cars. They never look the same, a couple have more of the brown junk on them, my guess is they are close to PCV flow.
20k miles on these? Did you buy these spark plugs from a Toyota or Lexus dealer?
It looks to me like the gap on most of these is way too wide...even the iridium tips seem to be missing (or really rounded). You need to confirm what I think I see, and if these are too wide or the tips missing, why.
20k miles on these? Did you buy these spark plugs from a Toyota or Lexus dealer?
It looks to me like the gap on most of these is way too wide...even the iridium tips seem to be missing (or really rounded). You need to confirm what I think I see, and if these are too wide or the tips missing, why.
Here's a pic of mine after 100k miles.
Yep 20k miles, and no I bought them off of ebay but they're OEM Denso units. Got the logo stamped on them along with the packaging. Hopefully I didn't accidentally buy knockoffs? If so they were very convincing.
These are Denso knock-offs manufactured in China that are designed to look like OEM's. Iridium tips don't disappear after 20k miles. Mine at 100k miles still had good tips. These were probably a good price initially, but really costs you later. I'm shocked you got 20k out of them. Have you had any misfire codes (P0300, P0302, P0304, P0306) to go with your P0430 code?
Buy 6 new plugs from the dealer. I order them online from McGeorge Toyota in Richmond Va. Much cheaper than my local Lexus dealer, even with shipping. Use the Toyota PN.
Install new plugs and see if your CAT code disappears. If not, your CAT may be clogged due to the spark plugs providing poor combustion.
Ebay plugs are almost always fakes only exception is if the seller is an actual Toyota/Lexus dealer. The ones in your picture are fakes you're lucky the entire plug didn't fall apart and rattle around inside your engine.
Ebay plugs are almost always fakes only exception is if the seller is an actual Toyota/Lexus dealer. The ones in your picture are fakes you're lucky the entire plug didn't fall apart and rattle around inside your engine.
Ash looking coating is from fuel additives.
Originally Posted by 93SCMax
These are Denso knock-offs manufactured in China that are designed to look like OEM's. Iridium tips don't disappear after 20k miles. Mine at 100k miles still had good tips. These were probably a good price initially, but really costs you later. I'm shocked you got 20k out of them. Have you had any misfire codes (P0300, P0302, P0304, P0306) to go with your P0430 code?
Buy 6 new plugs from the dealer. I order them online from McGeorge Toyota in Richmond Va. Much cheaper than my local Lexus dealer, even with shipping. Use the Toyota PN.
Install new plugs and see if your CAT code disappears. If not, your CAT may be clogged due to the spark plugs providing poor combustion.
Good luck.
WOW... no kidding! They even have "made in japan" stamped right on them. I'm calling local toyota/lexus dealers right now.
Thanks for helping me catch this guys!!! I'll swap the plugs ASAP and see what happens. I will report back soon!
EDIT: and no, no misfire codes. Car runs surprisingly decent but does blow some black smoke at high RPM, didn't think much of it!
Last edited by artfil91; Jun 24, 2022 at 12:00 PM.
