P0420 - Catalyst System Efficiency Below Threshold Bank 1

[ColinBarber]

It could well be an exhaust leak. You wouldn't normally get a fuel smell, unless the ECU is overfueling which it shouldn't do just because of that error. I'd check/clean the MAF sensor if you haven't done that already.

[is200 Newbie]

Check that the sensors that you replaced are tight and have not worked loose (worth a check) as this could cause an error and could cause a smell of fuel...

You can, only if the exhaust is cold, but your hand over a tail pipe and see if the noise gets louder or the engine stalls (with the car in park) - you may need 2 people to do this on both exhausts at the same time. If the car runs on with the exhausts blocked then likelihood there's a hole in the exhaust. It the hole is small in the exhaust it may cut out or it may struggle to hold the revs.

[BachelorDays]

How many miles have you driven since the last reset and what's the mileage on the clock?

The fuel smell could be from the EVAP valve or a leaky fuel cap. MAF always remains a possibility with this error code.

[H3XME]

Resurrecting an old thread. Did anything fix it or you just live with it? I have the same P0420 code, came on about 14months ago for the first time after I was revving its ti*s off in the snow. The car was running very hot, I think the cats just had it. I clear mine with OBD app and it stays off generally for good few weeks at a time. I can't say I've noticed anything different about the car at all, idle, fuel economy etc is all fine. 

[scudney]

Are you sure you haven't got a very small/tiny hole/leak near the lamba sensor🤔,had the same P420 error code when I owned my IS200 sport and had a custom made stainless exhaust fitted,it so happened that there was a very tiny hole/leak in the welding near the sensor that triggered the engine management light and P420 error code 🤔

[jackcramerr]

I got this error code today. 

 

[Texas]

Explanation here:

https://www.carobdcodes.com/lexus-p0430-catalyst-system-efficiency-below-threshold-bank-2.shtml
 

[sdposton]

Thanks to everyone for the info above, I had the same issue on my 2006 Lexus IS350.I was preparing for the worst and taking it to a mechanic where I'm sure they would have replaced the Cat and O2 sensors....  I thought I would check under the hood at the mass flow..... the connector was not on all the way!  plugged it in and fault was gone.  hope this helps you guys.