P0420 Code Resolutions

[hunter031789]

Just got a P0420 code on my way home from work. I've seen on here a lot of speculation between bad fuel, bad cats, and bad O2 sensors. I didn't see many long term updates or resolutions. Some even got repeated CELs after replacing the cats. Can anyone share what finally fixed their issue or seemed to have fixed it for the long term?

 

[sc85fiero]

In my experience, I have performed the desulfurization procedure that Ford published with mixed results. I have seen about 50% of those vehicles return and Ford says immediately put a cat in it. I will say however that I have had customers not want to purchase the Ford cat due to cost and availability and go with a cheaper aftermarket cat and have had very poor results with them.

Ford wants the catalyst oxygen storage value to be under .500, with bad cats I usually see them in the .700-.800 range. With aftermarket cats (cheap ones) I have seen them come back with under 5,000 miles on them with values in the .900 range.

I have not had any experience with some of the "higher end" aftermarket and performance vendors such as SPS to know how they hold up.

Long story short keep "good" gas in it, maintain your truck (poor oil change history can lead to excessive ring wear and other drivability issues) which can lead to catalyst contamination. If you get a P0420 or 430 it wouldn't hurt to try Ford's desulfurization procedure and if it returns (or doesn't help) I would go with a Ford cat or at least a higher quality aftermarket.

-Joe

 

[nikhsub1]

First, how many miles on the truck? I had my first P0420 at around 11k miles - no way a bad cat I thought. Ford tried to say the code was due to my intercooler and intake, I told them to **** off and to suckabagofdicks. I put SPD downpipes on. About 11k miles later another P0420. Now I was like WTF. I finally swapped out the downstream O2 sensor. Problem seems to be mostly resolved so far.

 

[hunter031789]

In my experience, I have performed the desulfurization procedure that Ford published with mixed results. I have seen about 50% of those vehicles return and Ford says immediately put a cat in it. I will say however that I have had customers not want to purchase the Ford cat due to cost and availability and go with a cheaper aftermarket cat and have had very poor results with them.

Ford wants the catalyst oxygen storage value to be under .500, with bad cats I usually see them in the .700-.800 range. With aftermarket cats (cheap ones) I have seen them come back with under 5,000 miles on them with values in the .900 range.

I have not had any experience with some of the "higher end" aftermarket and performance vendors such as SPS to know how they hold up.

Long story short keep "good" gas in it, maintain your truck (poor oil change history can lead to excessive ring wear and other drivability issues) which can lead to catalyst contamination. If you get a P0420 or 430 it wouldn't hurt to try Ford's desulfurization procedure and if it returns (or doesn't help) I would go with a Ford cat or at least a higher quality aftermarket.

-Joe

Thanks for the information, I'll have to give that a shot. I did JUST switch to 91 oct from 87 oct for the summer so I'm suspicious if there is a correlation. I think this is second completely premium tank I've run.

 

[hunter031789]

First, how many miles on the truck? I had my first P0420 at around 11k miles - no way a bad cat I thought. Ford tried to say the code was due to my intercooler and intake, I told them to **** off and to suckabagofdicks. I put SPD downpipes on. About 11k miles later another P0420. Now I was like WTF. I finally swapped out the downstream O2 sensor. Problem seems to be mostly resolved so far.

I'm at 89k miles. Is the downstream sensor easy to get to? Is that drivers side cat or the passenger side? I thought about giving that a shot before I went with a new cat. Would a new cat require welding or is it just two bolted flanges? I would crawl under there to take a gander but the skid plates would have to come off to see anything.

 

[sc85fiero]

P0420 is bank 1, passenger side on our trucks. The downstream 02 sensor will be on the cat itself, but it kind of faces upward so its a bit of a pain to get to. Im not saying its impossible, but the chances of a bad 02 sensor giving a catalyst efficiency code is rare. 02 sensors are reactionary and have a plethora of diagnostic trouble codes they can throw based on their readings and usually the 02 sensor isn't the actual fault. They read faults such as fuel trims being too rich or too lean, catalyst efficiency, etc.

The 2 exceptions to that are an oxygen sensor being contaminated (with oil, fuel, coolant, etc.) and circuit problems (usually from someone doing work and not placing the harness back in place and the 02 sensor lead melts to the exhaust). In those cases the 02 sensor itself must be replaced, even though it's not the actual cause.

As for your last question, the cat is just bolted on and no welding is required. Laying on your back it will be a bit of a pain because the 2 pipes are slid together with a clamp so when you loosen the clamp you still need to figure out a way to slide the one pipe out of the other that has been clamped together for the last 89,000 miles.

-Joe

 

[nikhsub1]

Yeah as mentioned this is on the passenger side - the O2 sensor isn't hard to get to at all IMO. It's a $50 part, you can start there and see what happens. If it is indeed the cat, the code will come again pretty soon. You could also try Cataclean https://www.amazon.com/dp/B07N7RZ5ZV/?tag=fordraptorforum-20

 

[hunter031789]

P0420 is bank 1, passenger side on our trucks. The downstream 02 sensor will be on the cat itself, but it kind of faces upward so its a bit of a pain to get to. Im not saying its impossible, but the chances of a bad 02 sensor giving a catalyst efficiency code is rare. 02 sensors are reactionary and have a plethora of diagnostic trouble codes they can throw based on their readings and usually the 02 sensor isn't the actual fault. They read faults such as fuel trims being too rich or too lean, catalyst efficiency, etc.

The 2 exceptions to that are an oxygen sensor being contaminated (with oil, fuel, coolant, etc.) and circuit problems (usually from someone doing work and not placing the harness back in place and the 02 sensor lead melts to the exhaust). In those cases the 02 sensor itself must be replaced, even though it's not the actual cause.

As for your last question, the cat is just bolted on and no welding is required. Laying on your back it will be a bit of a pain because the 2 pipes are slid together with a clamp so when you loosen the clamp you still need to figure out a way to slide the one pipe out of the other that has been clamped together for the last 89,000 miles.

-Joe

Thanks Joe, Great information, I really appreciate it! This gives me a lot to think about. I might start with changing fuel stations for a couple of tanks if the code comes back to eliminate that as a possibility. Rockauto doesn't list any OE cats so not sure what brand people would recommend.

 

[noorj]

+1 to start troubleshooting by swapping the downstream o2 sensor

Ford logic for catalyst monitor looks at the oxygen reading downstream during a fuel shutoff event to "measure" the amount of oxygen storage in the catalyst, catalyst oxygen storage correlates well with conversion efficiency of emissions. Therefore if the O2 is giving poor readings (reading lower oxygen than actual, lower voltage) this would cause the P0420.

If you're really looking to avoid swapping the cats/downpipes, the next options would 1) be to install O2 sensor defoulers which trick the system into thinking there is more oxygen storage than actual but wouldn't impact normal driving 2) desulfurization procedure Fiero mentioned which does generally improve cat oxygen storage but depending on the condition of cats can be temporary 3) weld in new O2 sensor bungs downstream of the whole catalyst - this gives the full oxygen storage capacity of both bricks of the catalyst to the system as the O2 sensor is reading downstream of both. A little harder to do but would certainly be cheaper than new OEM cats from Ford

Good luck!

 

[1BAD454SSv2]

Whenever i would fill up with Shell on my Gen 1 , i could pretty much countdown to get that code , 30 miles or so after fill up . I stopped resetting it . It would turn back off after about 100 miles