This sensor monitors the unburned oxygen content in the exhaust gases and feeds the data back to the ECU (electronic control unit, or electronic brain) in the car, which uses the information to decide how much fuel to inject into the engine. When the car gets older the sensor can become faulty. Sometimes but not always, the yellow engine management light on the dashboard will illuminate to warn the driver of the problem. (It is always worth having the code read however, as this issue is often the reason the light illuminates, but will not always be!) If the sensor is defective the car may fail the emissions requirements of the MOT test and be refused a test pass certificate. There are two oxygen sensors on the 6th Generation Accord. It is usually the primary sensor which becomes faulty. On the 1.8 this is located on the exhaust underneath the vehicle, just before (i.e. nearer to the engine than) the catalytic converter. On the 2.0 it is located in the exhaust manifold situated between the engine itself and the radiator. As a temporary fix, an injection system cleaning fluid added to the fuel, such as Forte Gas Treatment, might assist. The Accord is very particular about replacement oxygen sensors. It likes the genuine Honda item manufactured by NGK but may not work with many cheaper aftermarket alternatives. If you are lucky you might find an NGK version on the internet for around £80, or a second hand one from a breakers, but otherwise a Honda main dealer will charge more like £200.