I know the PO420 story & problem is persistent on these boards & in lots of trucks, but I haven't heard many success stories here, so I thought I'd share (since I'm happy about it), but will keep it brief.

2 new O2 sensors 2 years ago yielded an increasingly persistent PO420 in my truck. It had finally gotten down to about 100 drivable miles after clearing it that it would re-appear. Trying all the suggestions here EXCEPT a new cat yielded no results. Obviously, with the mileage on this truck, I'm not willing to pay a dealer for an OEM cat and/or labor to replace it.

After several tanks of gas and several hundred miles now, a new Magnaflow cat (self installed for a total cost of about $130) seems to have finally solved the problem. My truck does not have California emissions, so I cannot speak to that.

I'll delete this thread if it does come back to haunt me, but have hope. Sometimes the code should be taken at face value instead of beating around the bush.

 

On an non-cali spec truck, a single magnaflow cat will fix your P0420 code (provided the cat was actually the cause.....also could commonly be a rear O2 sensor or even a front O2 in very rare cases). The problem is cali spec trucks (which is some 99 and 00 trucks as well as all 01 and 02 3rd gens) which have the dual cat setup. I have heard of a case where someone used 2 magnaflow cats inline to solve the code on a cali spec truck but I haven't seen it repeated to verify that it would work in all cases.

 

good to hear, my CEL popped on briefly with that code last fall, cleared it and it never came back. we checked the O2 sensors with a scan tool and they were both working fine, so i was going to just buy a magnaflow cat when the light came back on, but it never did. still thinking that down the road this will help me out though, thanks for sharing.

 

I solved my P0420 problem (on a 2001 5VZFE) with this:
http://www.urdusa.com/product_info.p..._id=1230100014

 

Very good to know, especially with all those dam stupid idiotic meth heads stealing the cats from pickups these days. I was going to weld a cage around mine, but if the fix is only $130 then I can live with the fear of waking up to an extremely loud exhaust note.


Thanks for posting this!