Whats up everyone. I've been watching this forum for the last 4 years and I have this question maybe someone could answer.

Has anyone ever get a code 0420 "catalyst system efficency below threshold" before??? It comes on randomly. The cat is clean and passes smog no problem. Engine oil is changed every 3k. Spark plugs changed @ 110k. and the car currently has 168k. This code 0420 started happening around 100k. I checked the last emissions recall and my TL is past the dead line.

I was thinking that maybe a straight pipe could fix the problem. The problem got worse and it was throwing code 0420 all the time. So I went and bought a mil eliminator off ebay to fix the problem. Has anyone had luck with those mil eliminators. It still throws a code 0420. The O2 sensor is good by the way.

What do you guys think??

 

I am not sure about problem you are having but is not it time for some new spar plugs?
You have not changed it since 110k and you have now 168k?

 

might be dirty catalyst ..i would try sea foam..it will eventually clean your engine and your exhuast but wont hurt your o2 sensor