CAUTION! Avoid touching the Catalytic Converter(CC) when engine is still hot! It will take more than 4 hours for the CC to cool down after you stopped your car engine!
The oxygen content in the exhaust will rise due to HHO injection from any hydrogen generator. The more O2 found in the exhaust gas will be interpreted as fuel lean status by the Electronic Control Unit(ECU), which will cause more fuel to be injected into the engine. Thus it is necessary to trick the ECU into thinking that the engine is in fact having more fuel than needed within its combustion chamber, by fooling the computer to sense there is less O2 in the exhaust than there actually is. The O2 Sensor Extenter shown in this video is the most cost-effective Fuel Injection Enhancer(FIE) used to ensure your car can achieve the expected fuel economy after installing the HHO Electrolyser or Hydrogen Generator.
NOTE: The location and the number of O2 Sensor vary with the make of your car. This Video is just a guide.