All the vehicles have On-Board Diagnostics 11 (OBD-II) engine management systems to confirm the feedback loop from the oxygen sensor to the ECM by installing sensors at the pre-
Catalytic Converter and post-catalytic converter. While the first sensor is installed in the exhaust manifold, the second one is placed behind the catalytic converter; downstream sensor is heated and upstream sensor measures air/fuel ratio. That is, while they look like they do similar functions, the air/fuel sensor puts out a variable voltage signal that is an analog of the actual air/fuel blend in the cylinder, instead of a low voltage signifying lean and a high voltage signifying rich at the stoic point like the oxygen sensor; the air/fuel sensor voltage runs between 3.0 and 3.3 volts, depending on how much oxygen is hanging around During cleaning of these sensors some precautions are needed to avoid damage to the pigtail and the electrical connector, as well as to prevent any contaminants, including cleaning solvents from coming into contact with the part; the position of the silicone boot must also be correct. In the case of Oxygen sensor replacement, a proper procedure should warm the engine to ease pulling off of Oxygen sensor, the second step is to separate the negative terminal for auxiliary battery while the next procedure includes: turning off hybrid high-voltage battery, removing the radiator support cover lastly drain the inverter/converter coolant. Depending on the make, the air/fuel ratio sensor will require removal using the oxygen sensor socket, while the heated oxygen sensor will require unscrewing from the downstream exhaust pipe. Anti-seize compound has to be applied on the threads of the sensor to be installed, the electrical connector has to be connected again and the final step is a test drive to make sure there are no check engine lights on.