I just had my exhaust installed a few days ago and havent had any issues until today. My Check engine light came on, So I went to Lexus and the ran a diagnostic on it and came back with a code error P0420 "Catalyst System Efficiency Below Threshold (Bank 1). They are telling me its because of the new exhaust.

I have search on the forum and havent found much help. Does anyone know how to fix this? The cats were removed is this causing the problem?

I have a 2006 IS350

Thanks for anyones help.

Mike

 

it might help if you tell us what exhaust did u install

 

If the cats were removed, then yet, installing that exhaust caused the code. Did the main cats on the manifold get removed, or the rear cats in the mid pipe? If its the main cats, then yes, you caused the code, and you'd need to get O2 simulators to get rid of the light...

 

The cats buy the manifold were not removed just the ones midway. So o2 simulators need to be put in. Are they difficult to do and how long do they last?

Thanks a bunch, Mike

 

What exhaust did you install?

 

I think a more likely answer would be a damaged/improperly installed 02 sensor. Removing the secondary cats will NOT throw codes for any reason, there are zero sensors monitoring them.

 

I agree, the primary cats will cause a CEL if no sim is installed. People have removed the secondary cats as well as the resonator without triggering a CEL.

The o2 Sensor for Bank 1 might be the issue. Bank 1 is the passenger side sensor for a US spec vehcile.

 

I have a GHL Exhaust

 

These guys?
http://www.ghlmotorsports.com/

I'm not seeing any Lexus applications on the site

 

QFT. You have a damaged or contaminated O2 sensor after the first cat. I would check and see if someone managed to clog the air hole on the side of the sensor (it has to be able to get air inside to compare standard air with the exhaust via the zirconium thimble) or the sensor will not work. One greasy hand can screw up a perfectly good O2 sensor.

It's also slightly possible the shop forgot to reconnect the sensor when they did the work.

 

Hey Everyone thanks a bunch for all your help, This Forum has been the most informative of the 3 that I visit. Is there a way to test a o2 sensor to see if it is still good? (like you said about touching it and such).

GHL Motorsports did a prototype exhaust for my vehicle. As you see from the site they do alot with Audi, Corvettes, and other foreign vehicles.

The have been great as far as responding to my Issues, I am taking it to them to look at so we can get it worked out.

Thanks, Mike

 

There's no easy way to test an O2 for function without a device to plug into the ECM and check directly. I'd go for the obvious first - check the install, check the air hole, and check the wiring. If there's nothing obvious, then you'll need the laptop with the Lexus software to troubleshoot it - or you can just replace it and see if the problem persists. I doubt it would.