JUst checking since they dont sale the fake sensor anymore and on last truck the shop gutted it to save money when I bought it and it drove like crap and got bad mileage until I put new cats back on it . Thanks for input
Most vehicles have two upstream O2 sensors. These are located close to the engine, usually in the exhaust manifolds(one in each manifold). These are the sensors used to monitor air/fuel ratios.
Most vehicles also have two catalytic converters. There are usually two more downstream O2 sensors either in the catalytic converters or just behind them. These are just for emissions monitoring(they don't effect a/f ratios).
You do not do anything to the upstream sensors. You do the non fouler trick to the downstream sensors.
Some cars may only have one catalytic converter and if so likely only one downstream sensor.
My buell motorcycle only has one O2 sensor which is on the rear cylinder exhaust pipe. There is not one on the front cylinder exhaust pipe. And there is no catalytic converter so no downstream sensor(s). Just showing you there are different configurations. Either way, there are "upstream" sensors that you don't mess with and "downstream" sensors that are the ones that you would do this to.