So Ive been driving around with My CEL on for a while, it happened the day after I put on the exhaust, (Invidia N1), Ive Already got it tuned, and the tuner said the tune would not clear the code, My friend said hes had a similar problem on his audi s4, and what he did was put some washers in between his 02 sensor and the bung. But there is barely enough threads on my 02 sensor to put 1 washer. I was just wondering If anyone else has encountered this problem and solved it?
Seems like It might work if my problem is both 02's reading to close of a reading? Idk.... Thanks for any help in advance..



Here is what The code means:

Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

 

Hey man,

You need an O2 extender. This will fool the ECU into thinking the emissions system is working correctly. You have the CEL probably due to the fact you are using a high flow cat.

Like this one for example:
http://www.streettunedmotorsports.co...engine_fix.htm


-Bink

 

awesome man, thanks alot! that sounds like the fix!

 

Let us know how it turns out


-Bink

 

Go to the how-to section of the forum. There's a write up on fixing your problem with parts obtainable at any auto parts store. Problem most likely due to running a test pipe, although I had the same code with a high flow cat. The rear o2 CEL fix works. No problem since. Good luck.

 

I have a Speed Circuit test pipe which has an extension welded on for the 02 sensor and a tiny hole leading into the main tubing and it still doesn’t help. Sometimes the check engine light comes on, than it will go away for a bit. I found the only way it to get rid of it is running my Stage 2 Cobb maps which disables it.

 

 

My CJ lancer started to throw the same code a while after I replaced the OEM cat with a 200 cell high flow
You don't necessarily need to replace the catalytic converter to fix the issue.

Here's some info I put together
http://imgur.com/a/l3sDM2f

 

Very good source that you put together.

 

Can you tell me which 02 sensor do you put this on? Before the cat, or after the cat? I have a 2009 ES, and I’m getting P0420 code now. Thanks

 

After the catalytic converter

 

Thank you!

 

You won't believe this, but when I was going to install the spacer on the O2 sensor, I sprayed it down with penetrating oil expecting to have to fight to get it loose. As soon as I put the socket on it, it was already turning like wtf. I've never had a loose O2 sensor before, but I'm assuming that can cause the P0420 code to pop up as well.