P0420

[redkneck]

Ok, so my silverado is down for a bit waiting on a rear end. Got a CEL not long ago and scanned it. What's the most likely cause of this on my 5.3L?

[Goinghuntin]

This might help a little :cowboy:

http://www.obd-codes.com/p0420

Nathan

[Shaun_300]

Bad catylatic converters. P0420 is a Catylist Efficiency code.

[redkneck]

So you're saying it's the downstream O2 sensors that make the fault? Should I get a backpressure test or check the sensor, or just replace it?

[Shaun_300]

No it's not the sensors that are faulty, it's the cats themselves. If you get a P0420 that means the post O2's are doing their job. the only thing they do is monitor catylatic converter efficiency. As soon as they see the voltage go higher they flag the code, meaning the cats aren't breaking down the exhaust gases as efficiently as they should be. You'll have to replace the cats, they are part of the Y pipe.

[redkneck]

I get what your saying, and no doubt with the mileage they are due for a change.

[Shaun_300]

Yup, I've replaced a lot of them on vehicles with less than 100K on them.