I have an 06 IS250 AWD and I was driving down the freeway when a check engine light turned on followed by a "check VSC" I hooked up my ODBII reader to it and this code came out P0420 I read a few forums about this saying its either O2 sensor, bad gas, catalitic converter and engine coolant......has anyone experience this code?? HELP ME!!!

 

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. It worked for me.