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Ok I have been getting intermittent CEL for bank 1 threshold code. Replaced all O2 sensors but still getting it but only after about 30-40 min of driving 70-75 highway. Car runs fine but concerned what the ECU is doing after seeing that code i.e.making it Rich or going lean? Clear code and its stays good for a while then comes back up Car is 2012 with build date on Nov 11 with 37k miles. Any ideas or should I just drop big $$ on new cats. I want to keep it OEM as much as I can. Other than Ford who makes best direct fit cats?
 
Ok I have been getting intermittent CEL for bank 1 threshold code. Replaced all O2 sensors but still getting it but only after about 30-40 min of driving 70-75 highway. Car runs fine but concerned what the ECU is doing after seeing that code i.e.making it Rich or going lean? Clear code and its stays good for a while then comes back up Car is 2012 with build date on Nov 11 with 37k miles. Any ideas or should I just drop big $$ on new cats. I want to keep it OEM as much as I can. Other than Ford who makes best direct fit cats?
Bump:
 
If you're talking about P0420 (if you want some targeted help, it's always best to post the code which was omitted here entirely), when you're clearing the codes via scantool you're basically wiping the current emissions values. The Ford drive cycle for emissions testing is pretty much being on the highway for 30 minutes, hence why you keep seeing it. The car doesn't enter closed loop immediately (when it actually uses the O2 sensors for fuel trimming) and then you have to wait further for it to validate your emissions are working. If you replaced the rear O2 sensors (the ones that are validating that the cat is working) with known good sensors that have known good wiring to the stock-tuned computer without any breaks or faults in the connections all that's left is the cat. Since you've got a scan tool have someone sit in the other seat watching the live data view and see if the values look odd compared to the other bank.
 
If you're talking about P0420 (if you want some targeted help, it's always best to post the code which was omitted here entirely), when you're clearing the codes via scantool you're basically wiping the current emissions values. The Ford drive cycle for emissions testing is pretty much being on the highway for 30 minutes, hence why you keep seeing it. The car doesn't enter closed loop immediately (when it actually uses the O2 sensors for fuel trimming) and then you have to wait further for it to validate your emissions are working. If you replaced the rear O2 sensors (the ones that are validating that the cat is working) with known good sensors that have known good wiring to the stock-tuned computer without any breaks or faults in the connections all that's left is the cat. Since you've got a scan tool have someone sit in the other seat watching the live data view and see if the values look odd compared to the other bank.
Rear 02's replaced already. Driving car multiple shorter trips daily no CEL, only after driving continually for 40 +m or more speed is when this happens. I have had cats go bad before on other cars, fault code shows up pretty quick. I will see about getting a scan tool to see what shows up while driving
 
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@k98dave I feel your pain, I've been battling similar issues on my high mileage 2011 GT. The only things I know of that can cause the 0420/0430 codes are bad 02 sensors, an exhaust leak near the cats, or bad cats. If you've replaced all the sensors and don't have a leak, I'm pretty sure you need a new cat.

What caused the cat to fail is a more difficult question. Cats are usually advertised as being lifetime parts. But they can fail due to bad spark plugs, coils, misfires, fueling, bad injectors, oil blowby, a bad tune... a lot of things that can cause too much unburned fuel or oil to be absorbed by the cat. I am unclear whether a lot of track driving on an otherwise healthy and stock car can cause cats to overheat and fail - I've heard both yes and no on that question. It's just anecdotal but my experience is that several track friends with nice running and well-maintained track cars have had to replace cats with no other obvious problems. I was battling misfires on my car, which I think may have been part of the problem.

As @mwjscn mentioned, I think the fact you only get the code with extended driving is just a function of the oem software. My understanding is the ECU needs to see readings out of range for some length of time before throwing the code. I don't think it's a hardware issue.

If replacing cats, I probably would go with new Ford oem parts. I replaced mine with cheap aftermarket Walker cats and they didn't last, now I am dealing with this all over again. Good luck!
 
@k98dave I feel your pain, I've been battling similar issues on my high mileage 2011 GT. The only things I know of that can cause the 0420/0430 codes are bad 02 sensors, an exhaust leak near the cats, or bad cats. If you've replaced all the sensors and don't have a leak, I'm pretty sure you need a new cat.

What caused the cat to fail is a more difficult question. Cats are usually advertised as being lifetime parts. But they can fail due to bad spark plugs, coils, misfires, fueling, bad injectors, oil blowby, a bad tune... a lot of things that can cause too much unburned fuel or oil to be absorbed by the cat. I am unclear whether a lot of track driving on an otherwise healthy and stock car can cause cats to overheat and fail - I've heard both yes and no on that question. It's just anecdotal but my experience is that several track friends with nice running and well-maintained track cars have had to replace cats with no other obvious problems. I was battling misfires on my car, which I think may have been part of the problem.

As @mwjscn mentioned, I think the fact you only get the code with extended driving is just a function of the oem software. My understanding is the ECU needs to see readings out of range for some length of time before throwing the code. I don't think it's a hardware issue.

If replacing cats, I probably would go with new Ford oem parts. I replaced mine with cheap aftermarket Walker cats and they didn't last, now I am dealing with this all over again. Good luck!
I'm going to make sure I don't have any loose connections and check the exhaust pipe clamps for leaks as I read something about leaks causing issues. Car only has 37k miles but it is just over 10 years now by build date. I agree that oem cats would be best way to go.
 

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