Here's quotes out of the ECU manual about the O2 sensors:
If the front sensor or both front sensors have failed the owner may experience hesitation at speed, clearing when the accelerator is depressed slightly - rough running, particularly when first selecting drive and on change of load, heavy fuel consumption (resulting from open loop fueling
) and a black exhaust pipe.
If the rear sensor(s) fail then the owner may be unaware of it. There may be no driveability concern and only a reading with the vehicle Explorer will show the DTCs. (Vehicle Explorer is the name for the scan tool used)
If you have a good scantool, like my AutoXRay, you can watch this happen, and it's pretty cool. You can watch the code set for Catalyst below threshold, but still watch the front O2's switch, and watch the inputs from the MAF voltage and the air fuel ratio change with them, which doesn't happen when the vehicle is in open loop mode. When in open loop mode, it will not show the feed from the front O2's and other sensors at all.
So where can I pick up my new Mustang?????????
Just kidding man, that's why we're here, to learn about our cars.....