On ODB-II vehicles (96+), the ECU has two O2 sensors for diagnostic purposes. The first O2 sensor is located before the Catalytic Converter. This O2 sensor is responsible for all the Air/Fuel tuning and is imperative to the operation of the vehicle.
The second O2 sensor is located after the Catalytic Converter. The whole purpose of this O2 sensor is to ensure that there is a functioning catalytic converter in the system. The way it can detect this is to make sure that there is a difference in exhaust gasses between the first O2 sensor and the second. If the same exhaust reading is detected, then the ECU knows that there is either a damaged Catalytic Converter or no Catalytic Converter at all.
The ECU will then trigger a Check-Engine Light. On some instances, the vehicle will be thrown into a "Null" mode where the vehicle will not go over a certain speed and will be basically rendered useless.
This mechanical O2 fix is basically a way to space out the O2 sensor so that it still reads SOME exhaust gasses but it removes the O2 sensor from the direct flow of the gasses as to make the ECU believe there is a restriction in the exhaust gasses such as by a Catalyst.
There is NO GUARANTEE that this product will work on your specific application. There are always mixed results depending upon the layout of the exhaust system and the tuning of the ECU, however, this mechanical O2 fix is well known for eliminating most CELs caused by an O2 Sensor.
NOTE: There is no guarantee that this will alleviate your O2 sensor CEL. Some vehicles will need their ECU reset if the CEL is triggered before hand. This Spacer may cause a clearance issue as it spaces the O2 Sensor 36mm (1.43") further than the base of where it seated.