Exhaust Flap shorting out - Check Engine light

[GrimSniper]

Evening everyone!
SO i bought this 2019 GT PP1 back in Sept of 2025. it does have aftermarket long tube headers and a Corsa Extreme Exhaust with the flaps to make it louder/quieter. I live in PA and its my daily driver currently. About Oct or November i started getting a check engine light for an O2 sensor, took it back to where i bought it from, they said the car has a tune so they cleared the code and we waited to see if it came back. (I now know the car is tuned for 93 and E85, tho idk thru who) Anyways, the light comes back, i take it back to the garage, they clear the code again. Light comes back on the same day, im frustrated so i drop the issue and figure ill wait till nice weather before i fix the issue. Now i have a code for an electrical fault for the one of the exhaust flaps. I called the garage today to get it scheduled for both issues, they are telling me about $300 to replace the O2 sensor without knowing which one and they will try to find the wiring fault for an hour. If they cant find it then they will probably send me to a Ford dealer.
Would anyone be able to help me out? Either with easy things to check for or anything before i go to the garage. I dont have a place that i can get the car in the air to look underneath (which is why i called the garage). I also came from a 2015 Focus ST and i know if you tune them, then you usually have to get a defowler for the O2 sensors as well. Is that the same for these 5.0s? Any help is appreciated. Im not new to cars, been raised on Ford by my Dad and i do basic maint and do car shows, but im also not a certified mechanic. Im in the IT world haha.

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[blankman]

I don't personally have LTH , but was researching info about them on this forum. If memory serves me right, there is a chance you might have to run them to clear those codes.

As far as the active exhaust valves go, did the car come from the factory with them? Apparently it is a known thing where the wires leading to the connectors can get to close to the exhaust itself and melt and fray the wires to the connector. That may be a starting point to look for before you take it to a shop.

 

[GrimSniper]

I don't personally have LTH , but was researching info about them on this forum. If memory serves me right, there is a chance you might have to run them to clear those codes.

As far as the active exhaust valves go, did the car come from the factory with them? Apparently it is a known thing where the wires leading to the connectors can get to close to the exhaust itself and melt and fray the wires to the connector. That may be a starting point to look for before you take it to a shop.

Yes sir, it did come factory with them. ill def check there to start with

 

[BullittBoy]

Do you have cats? If YES, then what exactly are the O2 sensor code/s? Is it P0420 and/or P0430?
I would not pay someone 300 bucks to change out a O2 sensor, especially since they don't really know if it is bad? It is SUPER easy to swap them yourself.

Need to know what the codes specifically are. Sounds like this shop is just spending your money with no real root cause for the issue causing it to pop codes.

I also came from a 2015 Focus ST and i know if you tune them, then you usually have to get a defowler for the O2 sensors as well. Is that the same for these 5.0s?

YES-That's what P0420/0430 means, Bank 1 and 2 cats are not efficient i.e. the cats are not working to the level the ECU expects to see. I had a FOcus RS and when I put on a modified down pipe and ditched the cat, same issue. Before you spend any money to a shop, try that, especially if those are the codes you are getting.

 

[Cobra Jet]

Evening everyone!
SO i bought this 2019 GT PP1 back in Sept of 2025. it does have aftermarket long tube headers and a Corsa Extreme Exhaust with the flaps to make it louder/quieter. I live in PA and its my daily driver currently. About Oct or November i started getting a check engine light for an O2 sensor, took it back to where i bought it from, they said the car has a tune so they cleared the code and we waited to see if it came back. (I now know the car is tuned for 93 and E85, tho idk thru who) Anyways, the light comes back, i take it back to the garage, they clear the code again. Light comes back on the same day, im frustrated so i drop the issue and figure ill wait till nice weather before i fix the issue. Now i have a code for an electrical fault for the one of the exhaust flaps. I called the garage today to get it scheduled for both issues, they are telling me about $300 to replace the O2 sensor without knowing which one and they will try to find the wiring fault for an hour. If they cant find it then they will probably send me to a Ford dealer.
Would anyone be able to help me out? Either with easy things to check for or anything before i go to the garage. I dont have a place that i can get the car in the air to look underneath (which is why i called the garage). I also came from a 2015 Focus ST and i know if you tune them, then you usually have to get a defowler for the O2 sensors as well. Is that the same for these 5.0s? Any help is appreciated. Im not new to cars, been raised on Ford by my Dad and i do basic maint and do car shows, but im also not a certified mechanic. Im in the IT world haha.

See if any of these threads may be of help to you RE: active valve actuator issues/fixes:

https://www.mustang6g.com/forums/threads/mustang-gt-active-exhaust-controller-standalone.179782/

https://www.mustang6g.com/forums/threads/active-exhaust-diy.153146/#post-3259535

https://www.mustang6g.com/forums/th...ust-install-guide.101913/page-43#post-3176423

https://www.mustang6g.com/forums/threads/active-exhaust-diy.153146/#post-3122899

 

[GR1MxREAPER]

Might be 2 seperate issues. The active exhaust lights are super common, and an easy fix. Go in the back and by the motors look at the electrical harness for the active exhaust, what happens is your exhaust moves backwards a little when you floor it and that harness can get pinched inbetween the exhaust and the pinch weld on the back of the car. Make sure this hasn’t happened and you don’t have bare wires. The fix is wrap the bad spot with electrical tape and loose your exhaust around your x pipe or wherever and push it towards your engine a little bit so it doesn’t happen again. Guessing that could be your problem, worth a look atleast as it’s free and easy to see.

 

[GrimSniper]

Hey guys

So the codes are the 0420 and 0430 - so i assume there is no way of getting those to go away?

As for the active exhaust issue, the garage did say that one of the connectors got corroded (probably due to driving in the winter) and its $130 for the wiring harness.

Any suggestions on either?

 

[2015 Silver GT]

Hey guys

So the codes are the 0420 and 0430 - so i assume there is no way of getting those to go away?

Those are the codes for your catalytic converters. First question is do you even have them?

 

[GrimSniper]

Those are the codes for your catalytic converters. First question is do you even have them?

If im honest, I haven't seen under the car. I know it has aftermarket long tube headers and exhaust.

 

[NGOT8R]

The active exhaust wiring harness on the passenger gear side is usually the culprit. I had first hand experience with this on my 2019 Bullitt. Replacement harnesses were on backorder at the time, so I de-pinned and soldered mine.

See post #9 here.

https://www.mustang6g.com/forums/threads/active-exhaust-failure.134702/

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