First off I have a 06 IS250 AWD with 100,967 miles on it.
I (as a female) have replaced my spark plugs with help from this forum, learned to change my own oil and replace front brakes. I do have a great helper in my brother in law to show me the ropes.

I have 2 codes with the VSC CEL on currently. One is the P0420 bank 1 Cat converter operating below threshold. and Ignition coil B.
The ignition coil is easy enough after doing the spark plugs; however, the O2 sensor is proving more difficult. I have searched and searched the forums for a DIY. I find a lead and it turns out to be a different model or the search leads me to a totally different forum than IS-second generation. I was hoping someone could lead me to the correct spot OR put a DIY here to help others in my same boat. Thanks in advance. I spend hours on here reading all your tips.

 

I beleave with the p0420 it's either driver side cats bad, o2 sensor under the driver side on the mid pipe, or exhaust leak in between. Try to replace the coil first then see if the other code still there.

 

Dealer states Bank 1 is the passengers side.

Let me simplify...
Looking for a Bank 1 O2 Sensor replacement DIY for IS250 second gen.

I am also thinking it could very well be an exhaust leak but still need a DIY for the O2 sensor.
I do appreciate your quick response.

 

I've had the P0420 code come up twice. The first time it went away by itself after a few days and didn't come back for a couple of months. The second time, I cleared it with my scanner, and it hasn't come back thus far. That said, I'm sure it's only a question of time before the code changes from intermittent to persistent, and I have to change the sensor.

I'm also hoping someone does a DIY writeup, or at least an explanation of how to unplug the O2 sensor. There are a few threads on the forum about how to use the special tool to unscrew the sensor from the mid-pipe, but none mentions how to disconnect it electrically. I hope you don't have to remove the seat to get to it.

 

If it's the cat on the header itself best to take it too a shop. As when replaced my headers for ppe it's a 6hr job. Not easy. Now if it's the sensor you can get it from the top but it's a tight fit.Bichon yes on the secondary o2 seat has to be taken out 4 bolts,door sill comes off, panel were left of the ebrake, dead foot rest, and then the carpet pulled back. Then you'll see were to disconnect the o2 30min job.

 

[QUOTE=Bichon;7042277]I've had the P0420 code come up twice. The first time it went away by itself after a few days and didn't come back for a couple of months. The second time, I cleared it with my scanner, and it hasn't come back thus far. That said, I'm sure it's only a question of time before the code changes from intermittent to persistent, and I have to change the sensor.

Bichon, Exactly what happened to me. I have to inspect and do emissions in April so I need to finally fix the problem. It is more persistent now only going off for a couple days and returns.

 

I was aware of the carbon build up issue so when I started getting a P0420 trouble code to routinely come on after 77k miles (came on 6 times between 77k and 81k miles) on my '06 IS250 AWD (catalyst system efficiency below threshold bank 1), it was time to take it to Lexus and argue that the carbon build up is causing the rough idling and is also damaging the cat, causing the trouble code to pop.... They wouldn't confirm that the cat was under warranty to 80k miles like I've seen in other posts, but They did acknowledge the carbon build up issue and replaced the pistons and decarbonized the cylinder heads, etc. And also replaced the failed cat as a goodwill gesture. I was very satisfied with how the dealership handled this issue, especially because it did not cost me a dime! Apparently the engine is covered under a nine year Lexus warranty. Try to take advantage of the carbon build up TSB and argue that it's damaging the cat.