Recently had my 2006 IS250 with 83,000 miles display the dreaded vsc twice in a week, I noticed it would do this when accelerating uphill in our dales here in sunny England I decided to investigate and code read the car it generated a P0420 code Catalyst below efficency below threshold Bank 1. Bank 1 is the right of the V6 when sat in the drivers seat facing forward this does not matter if you are LHD or RHD vehicle.








My car ran great otherwise and after clearing the code I noticed it would not come on driving on a level road so the hills were opening a gap in the exhaust.

I jacked the car up and saw the clamp on the shield had corroded and been rubbing on the exhaust no noise noted from rubbing ie rattle etc but it must have fatigued through.

I figured that the downstream oxy sensor which monitors cat performance must be seeing air getting in and it deduced the cat was faulty.

So I removed heat shields and cleaned pipe applied a sealing paste and a universal split repair tube see pics . I will apply a permanent fix when a two post lift comes available but I am confident it will last some time.

So now no leak and no more light on .

I will monitor and see how long it lasts .

 

I had similar issue, fixed after welding exhaust leak....Rusty pipe as well.

 

How has the repair held up so far? My wife's car keeps throwing this code, so I have to get underneath the car and check.

 

So far it has been ok I even think it has improved running a little but that may just be me.
I have had no incidence of the CEL for about a week now.