Whats up CL, I have a 01 GS430 with 93k it has a P0420 Check Engine Light. It said - Catalyst system efficiency below threshold bank 1. that keeps coming on and off. Im pretty sure based on experience and searching that changing the faulty O2 sensor would fix this problem but im just wondering if you guys think its worth changing all 4 O2 sensors instead of 1 only while the mechanic is already in there. What are the chances of me changing 1 and then another failing? I hear some are alot harder to get to then others. Can someone tell me what type of labor I should be looking at to pay someone for the CEL P0420 Catalyst system efficiency below threshold bank 1. Thanks everyone please let me know.

 

I'd only replace the one. and I wouldn't have a mechanic do it, it's so easy to replace them, vs. paying a person to do it.

 

Had exact same problem as you did, same code. Have an 02 GS430 with 111,000 miles. Light came on at around 99,000 miles. Folks and dealership told me it was bad cats or exhaust leak. Proved to be neither. I replaced the downstream 02 sensor or bank 1 (driver side) and replaced all of my spark plugs. I suggest you do the same along with the spark plugs. Light has been gone ever since. Get the Denso 02 sensor from Amazon. Only about 60 bucks as opposed to getting from dealership.

 

Search...... Multiple threads about this

 

Well SUPPOSELY the person who sold me the car just did the spark plugs not too long ago so they're definitely good but I will go ahead and change that O2 sensor since you said you changed one and it fixed our problem. Can you tell me which one I need for Bank 1 milellie? Denso 234-4630? Denso 234-4138? or Denso 234-4623? Im so happy you had the same problem as you just made my day since I dont have to change all of them. Whats funny is I was reading your other posts about how you wanna sell the car because you hate the way it drives. It seems like we were having all the same problems but changing ball joints fixed most of my steering issues, did you try that?

 

your mechanic already messed up your ABS line and said its gunna happen anyways after changing your LBJ. you really want him to do another job on your car?

 

No im gonna have someone else do it. Is Bank 1 the upstream or downstream, one thread tells me upstream but milellie said its downstream? im really confused, a part number for the one I need would help and please tell me how long the labor is to change the O2 sensor so I dont get ripped off. Thanks

 

But I did search it online my mechanic is right you cant get the ball join out without a hammer or a press, the press kills the tie rod and the hammer has a chance at destroying an old ABS sensor, he didnt do anything abnormal so he is believable. not EVERYONE breaks the ABS sensor but it happens. What do you think he could have did differently to not break it?

 

ive yet to damage a tie rod nor damage the ABS line when doing 2 GS's LBJ change

what do i think he could have done differently? work carefully.

anyways off topic but yea. regarding o2. I dont know .

 

2001 gs 430 - 139k!!!. Replace both pre-cats at the same time. you may find it difficult to remove either one and need some heat! Happened to me, one would not budge without the Heat. Any good muffler shop can do this cheeply. paid 50 bucks for removal and install. i used the denso sensors. ordered of Amazon, no sales tax and free shipping.

best of luck

 

I got a check engine light this morning as well and it was also a p0420. I scanned it at work and cleared it, if it comes back on ill monitor my sensors and see if its a bad sensor or a bad cat. Well wait and see I guess

 

I bought both Denso 234-4623 and 234-4623. Got 234-4623 replaced and that did the trick.
I would buy both to save some hassle. If you don't need 234-4630, you can always return it back to amazon.

Yep. still hate the way it drives. I've replaced just about every OEM suspension part on this thing with OEM.lol. Still loose steering and non precise and follows the road and steering wheel tilts while going over bumps.Ball joints,tie rods,control arms blah blah blah. Care continues to wear out tires. Suspension still makes squeaking noises. Dealership said my driver side balljoint is loose. Weird since i just had it replaced less than 6 months ago!!

 

Most likely it was just your sensors. Waste of money replacing your Cats.

 

Milellie did you try changing your steering rack bushings. Im almost certain yours has play like mine does. I bet that would work, if not then its DEFINITELY the wider/bigger 17" wheels and low profile tires compared to the 16" 215/60s this car was originally equipped with. Let me guess you have the 17" lexus rims as well with the 235/45/17 tires? if its not the steering rack im GUARANTEEING its the rims and tires because ive experienced this with another car when I changed the rims, i went crazy thinking something was wrong changing everything for nothing meanwhile just putting the stock rims on the car fixed everything. Let me know im curious

 

And you listed the same part number twice
"I bought both Denso 234-4623 and 234-4623. Got 234-4623 replaced and that did the trick.
I would buy both to save some hassle. If you don't need 234-4630, you can always return it back to amazon."

can you clear that up for me so I know which one to order and replace first. Thanks