Can Exhaust Sensors Be Turned Off?

93lx5.0

Founding Member
Mar 1, 1999
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Fairfax, VA
I purchased my GT500 a few weeks ago, and love the hell out of it. The thing is a monster!! But twice now I have taken it to get the emissions tests, and twice it has failed because they don't get a reading from 3 monitors when they plug it in. At first they told me to drive it for 80-100 miles or so to reset the sensors, but I did that and brought it back the 2nd time with the same result. The monitors that are the issue are the Catalyst (CAT), The Oxygen Sensor, and the Heated Oxygen Sensor. The car is definitely not stock (mods in my sig), but unfortunately it didn't come with a tuner. As far as I can tell, there is a catted midpipe in there. Could there be a custom tune that turns off those sensors for some kind of performance gain? Would I need to buy a tuner and a custom tune and replace what's on there? Thanks.
 
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I purchased my GT500 a few weeks ago, and love the hell out of it. The thing is a monster!! But twice now I have taken it to get the emissions tests, and twice it has failed because they don't get a reading from 3 monitors when they plug it in. At first they told me to drive it for 80-100 miles or so to reset the sensors, but I did that and brought it back the 2nd time with the same result. The monitors that are the issue are the Catalyst (CAT), The Oxygen Sensor, and the Heated Oxygen Sensor. The car is definitely not stock (mods in my sig), but unfortunately it didn't come with a tuner. As far as I can tell, there is a catted midpipe in there. Could there be a custom tune that turns off those sensors for some kind of performance gain? Would I need to buy a tuner and a custom tune and replace what's on there? Thanks.


I've no idea what resetting an 02 sensor would look like. As far as I know, they either work or they don't work. They may just need to be replaced but if that were the case, it should be spitting out codes and you should have a Cel light on.

Chances are that you do have a tune of some sort. Maybe someone more familiar with your year knows of a way besides going to dealership to find out. I don't believe that the sensors can just be deactivated through a tune but can however, be ignored (I could be wrong about this part).

If you know that the x-pipe is after-market then it's a forgone conclusion that something was done to the tune to make the EEC happy with the change.


Do you have an OB2 code reader? You might want to get one and I would DEFINITELY purchase a hand held tuner for that car if for no other reason than to ensure that you can undo anything that might happen at dealerships etc. I would be careful about popping into the dealership to have them check too. I'd be concerned that they would inadvertently flash the existing tune without knowing what's in it then be unable to fix the mistake.

Are there any Mustang performance shops near you?
 
Is the engine light on. If not car has a tune. I no my buddy has a 2010 and he can't turn them off. If there is no engine light on and u failed the emissions. What was the reason on the emissions statement. It's prob that the readiness test aren't complete. It won't pass until they are. The O2 sensors need to be turned back on
 
Who did the tune? If the person u bought it from kept the tuner u might be out of luck. It's married to the car. Than u have to go to the dealer and have them/pay to put it back to stock. Than buy a handheld tuner and than take it to a tuner with a dyno.
 
. I believe depending on what tuner/programmer you would get, you can put a canned tune into the car without the stock tune. Just like having a race tune in the car and than putting in A street Tune. I do this to pass my emission test without having to upload the stock tune and than put in the emissions tune. Basically. Buy a tuner with a canned tune for say a cai or 93 octane. Load it into the car, the tuner should save the tune that's being removed. If it doesn't u need to bring the car to a dealer with the programmer you want/bought have them install a stock tune for the car and after there done with that immediatly install the 93 octane tune. That way the programmer is married to your car.
 
Were it me, I would do myself a favor and buy a tuner from Ford.

They will likely flash you back to stock before applying any of the Ford performance tunes.

A quick way to find out for sure is to call one or two of the dealerships in your area to see what they have on hand. A work mate of mine not all that long ago ditched a Bully Dog tuner for his Ford Diesel. He bought the Ford unit to replace it with. That is what they did to his vehicle. His emissions alteration was ALSO the removal of the cats.

What Ford will NOT do is remove the cats for you. Much of that depends on the laws in your state. You may have to reach out to a Ford dealership outside of an emissions controlled county or put cats back on before they will touch it but I'm not 100% sure on this portion. There were no emissions enforcement in the county that we were in.
 
Tuners can turn the Rear o2 sensors off. They are not really needed for anything other than emissions to make sure the cats are doing their job. If you are happy with the current tune that is on the car then you can buy a tuner from say Bama or anywhere that offers canned tunes and simply have them supply you a tune for your mods with the sensors turned on. Doing this will store the current tune that is on your car as the "stock" tune so if you revert back to stock it will simply put your current tune back on there. Keep in mind if you go this route and have the o2 sensors turned back on you will have to but some drive cycles on the car so you can pass emissions. You can't simply turn them back on in the parking lot and drive up to have it tested.

Long story short. If you like your tune then just use that as your "stock" tune on a handheld tuner and get a canned tune to turn the sensors on for emissions testing.
 
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It would be a pain in the ass, but I'd go the extra mile and try to track down the previous owner. If they had the car tuned with their own programmer, it's locked to the car (and is otherwise useless) so they should be willing to part with it. It's important to know what has been done to your vehicle and to have the ability to return the car's tune to factory. Switching off the car's down stream O2 sensors is very common on aftermarket H or X-pipes, even if they are catted.
 
I had the 02 sensors on my 11 turned off for 2 1/2 years. ( turned off in the tune )
After the headers & high flow cats, ( Kooks ), were installed, it threw codes, so the tuner turned them off. The car was due for inspection in July 2014, ( N.J. ), to pass, everything has to be enabled. In June, I had Kooks " green " cats installed, and the 02 sensors turned back on. The car passed inspection with no problems.
You need to get hold of the previous owner & find out what was done to the tune..
.............................Good luck !
 
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