P0420 even after rear o2 replacement

[Bpjr07]

Hi guys I need some help.
Bought the car preowned with 17k 2 years ago, at 25k the check engine light would light up for a day or 2 every month, at 40k it would be pretty much be on all the time off 1-2 times a month. Did nothing because it ran great, get 32-33 mpg, I just check the light once a month to make sure it was only p0420. (My cheap scanner says it's the sensor 1 bank 1, is this because it's a universal scanner?)

My Gut tells me previous owner probobly had bolt ons and tune giving the bad o2 or bad cat(does not smell bad)? Car came with k&n filter, cobb rear motor mount, blowoff valve, the stock exhaust was rewelded a foot downward from the Cat.

Now at 50k, the rear o2 and 1 hour of driving and the code popped up permanent again.

Anyone have had this issue? I was thinking of trying a non fouler but on inspection it will be able to be seen from the top of the engine bay, failing visual.

 

[SteveS]

It's usually the O2 sensor upstream of the catalyst.

https://www.700r4transmissionhq.com/p0420-ford-fiesta/

 

[Ford ST]

Definitely don't agree with the upstream sensor being the one that normally triggers that code. Is it possible sure but in my experience from diagnosing, and my experience from automotive School it is the downstream sensor if it is actually a sensor. The number one reason why that code happens is because of a catalytic converter but definitely not always.

Since this car was modified does the car have the original catalytic converter?

Catalytic converters have a federal warranty on them I believe it's 8 years, or 80,000 miles. If it is the original catalytic converter you could get it replaced for free. You may have to pay a diagnostic fee at the dealership definitely worth it.

Sent from my LG-LS997 using Tapatalk

 

[pirite]

p0420 is bank 1 catalyst under efficiency.
monitor the b1s2 while driving at a cruise after its up to operating temp. if its jumping around the cats bad.
thats all i do at work for p0420. just depends on what the rear O2 sensor sees as far as if the code trips or not.

 

[TyphoonFiST]

If I was you...Id buy a bottle of this and give it a whirl. I've had a lot of people have that code and did this product with success. Its worth trying Vs Cat replacement. Good luck and keep us up to date!

https://www.amazon.com/Cataclean-12...d=1614750782&sprefix=CATACLEAN,aps,187&sr=8-4

 

[TyphoonFiST]

Rear O2s seldomly go bad....The upstream O2s get the most abuse. .FYI. Or it could be the quality of gas your state uses in winter time as the additives in them can trip with P0420 code even thought the system is OK. What month does this happen also? Is it ok for summer months? Then the winter time comes and it trips again?

 

[Bpjr07]

I live in california no winter blends. I use only 91 chevron or 76, I add a full system techron cleaner every oil change.


Think the guy before me probobly had a tuner and had exhuast pops too, when I bough it car had plastidipped red wheels, side mirrors and spoiler.i dont know if the car is tuned to be honest. How can I find out?

I replaced the rear o2 sensor 30$ cheap, but not fix it, I will check out that cat cleaner, it's worth a shot. I will see if my programmer does live data logging.

As for ford warranty.... looks cat stock but since the catback was removed and rewelded I feel like they will claim it on user fault. They will want charge me 2-400 dollars just to blame it on me. I can put that money toward a replacement high flow cat?

Thank you all for the input.maybe the cat clean will work since the code is off a few days out of the month.

 

[TyphoonFiST]

You should also use a GDI specific injector cleaner that is formulated for Direct injection not just any injector cleaner* There are a couple out there ..... Here area two specific for GDI and safe for Turbo and superchargers

https://www.amazon.com/STP-Direct-Injection-Injector-Cleaner/dp/B071Z6GPRN/ref=sr_1_3?crid=1YMER1XRF4DE8&dchild=1&keywords=stp+direct+injection+fuel+injector+cleaner&qid=1614819204&sprefix=stp+direct+,aps,187&sr=8-3

https://www.amazon.com/dp/B06X95H7K6/ref=twister_B081TRRB26?_encoding=UTF8&psc=1

 

[Ford ST]

Very odd someone would have to weld anything. No cat back exhaust system requires doing any damage to that area. Maybe the person made some type of homemade system.

Just so you know high flow cats can still trigger a code.

I would recommend posting some pictures.

Sent from my LG-LS997 using Tapatalk

 

[Bpjr07]

The front o2 sensor is pretty expensive.

Very odd someone would have to weld anything. No cat back exhaust system requires doing any damage to that area. Maybe the person made some type of homemade system.

Just so you know high flow cats can still trigger a code.

I would recommend posting some pictures.

Sent from my LG-LS997 using Tapatalk

I will try to get under the car and take pictures, the cat is factory bit I did think the cut was odd.
Think a kid originally bought the car added Bolton's and a tuner and cut the exhuast of after the cat?

 

[Snrub]

I've had a P0420 multiple times on previous cars. It was always the cat.

 

[Bpjr07]

If I was you...Id buy a bottle of this and give it a whirl. I've had a lot of people have that code and did this product with success. Its worth trying Vs Cat replacement. Good luck and keep us up to date!

https://www.amazon.com/Cataclean-120007-Complete-Exhaust-Milliliter/dp/B002BVXM92/ref=sr_1_4?crid=3HDFKI28A7XE3&dchild=1&keywords=cataclean+catalytic+converter+cleaner&qid=1614750782&sprefix=CATACLEAN,aps,187&sr=8-4

Progress report Update!

I threw in the Cataclean at about 1/3 tank. Drove it pretty hard around town for a 45 min. Then on the highway for another 45 min. Tank was Close to red when I filled the tank up.

People usually reset or disconnect the battery to see if it works. I just kept driving it and have It naturally come off if it did work.

Poured Cataclean 60,500 miles
At 60,660 miles the check engine light disappeared and has been off the last 200 miles!

Thanks TyphoonFIST!

 

[Dpro]

I live in california no winter blends. I use only 91 chevron or 76, I add a full system techron cleaner every oil change.

Ah excuse me we have Winter blends in California look it up on the CARB website.
In fact thats why our gas prices always jump and down. They do not stockpile gas here they make it on demand and change it up season wise. We are right now switching over to Summer blend and also because Texas like clockwork our prices have gone up again.
Any excuse they can find to raise the price they do.

 

[Bpjr07]

Ah excuse me we have Winter blends in California look it up on the CARB website.
In fact thats why our gas prices always jump and down. They do not stockpile gas here they make it on demand and change it up season wise. We are right now switching over to Summer blend and also because Texas like clockwork our prices have gone up again.
Any excuse they can find to raise the price they do.

Well that's News, to me though it was only for freezing climates, thanks for the info