Q: o2 sensor

If you are referring to 1991 model years of the Accord versus the Civic, the principal difference is the Accord used a heated oxygen sensor while the Civic did not. To compare and contrast Toyota sensors, I would need a model year and model. Broadly, across models, the principal of operation of these oxygen sensors is identical. The sensor simply produces a voltage output that is proportional to the amount of oxygen contained in the exhaust stream. That voltage output provides the necessary data input to the engine computer to optimize fuel delivery (minimize fuel consumption and minimize emissions). The differences between the sensors are principally in the mounting and case and whether the sensor has an internal heater (all newer ones are heated). Oxygen sensors are easily tested using an appropriate automotive scope which can measure and graph the sensor output. Finally, these sensors do wear out and indeed the sensor will often degrade enough to warrant replacement well before the check engine light will come on, signifying total failure. If you desire an inspection of these sensors as they exist on your car, please request O2 sensor diagnostic/replacement service and the responding certified mechanic will carefully test the output of your sensors. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.