Q: after replacing spark plugs and wires engine light still come on should i replace the O2 sensor as diagnose suggested if so which

Hello. If the scanner indicated the O2 sensor was bad, I would recommend replacing. The oxygen sensors are located in the exhaust system of the engine, and they sense the oxygen content of the exhaust gases. There should be two O2 sensors on this model engine, one on either side of the catalytic converter.

The sensor located just in front of the catalytic converter measures the mixture of the exhaust gas exiting the engine. The sensor located after the catalytic converter is used to measure the performance of the converter by comparing the O2 levels before and after. (Upstream is the same as pre-catalyst, before the catalytic converter. Downstream is post-catalyst or behind the catalytic converter). The amount of oxygen in the exhaust varies according to the air/fuel ratio of the fuel injection system. The oxygen sensor produces a small voltage signal that is interpreted by the electronic control unit (ECU) of the fuel injection system. The ECU makes constant adjustments in fuel delivery according to the signal generated by the oxygen sensor in order to maintain the optimum air/fuel ratio. If you would like to have this done, a certified technician from YourMechanic can come to your car’s location to replace the oxygen sensor if needed.