What Is A Po420 Cel Code?

[95WTSI]

So I was setting my boost controller this morning and set it a little too high. I hit 20 psi for the first time and WOW !!!!! anyway, I got a CEL for PO420 catalyst system efficency below threshold. can I just turn that off and not worry about it?

thanks!!

 

[siceclipse]

clear the code. if it comes back its most likely your o2 sensor.

If this has helped please assign me a positive reputation point.
thanks.

 

[akdsmer]

clear the code. if it comes back its most likely your o2 sensor

It could be a bad O2 sensor. If it was a PO139, then it would most likely be your O2 sensor. P0420 is catalyst efficiency. This code is set when the PCM sees the Post catalyst O2 sensor signal signal mirror the upstream O2 sensor signal. As the catalyst is designed to chemically convert the Oxygen in the exhaust into Carbon Dioxide, there should not be as much Oxygen after the catalyst for the rear sensor to detect and so the voltage will not be the same. The second signal actually is more of a flat line rather than a sine-wave.

Putting a bigger load on the engine creates more heat, and allows the sensors to actually work better. The catalyst on the other hand has to work much harder as there is more fuel to convert (if your not running lean!).

With that in mind....Check the voltages of the two Oxygen sensors. If the rear (post-catalyst) sensor signal is cycling (usually 100mV to 800mV) with the first sensor than the sensors are working and the catalyst is not (this is quickest done with a scan tool-best done with a labscope). Catalyst efficiency is a two-trip monitor which means it should need to see this on two sequential trips to throw this code, not just your first hammer down.

That is the official rhetoric for an understanding of the code. Same as Siceclipse, I would clear the code first and see if you can get the code to reset.

 

[95WTSI]

I figured that is was the O2 sensor, but wanted to make sure. Thanks for the info and the responses!!