2002 Honda Accord SE O2 Sensor?

the primary o2 sensore is before the cat, the secondary (if your car has one) is the one after the cat.

It isn't difficult to change if you can see it. Which sensor did he tell you that you need? If it is the front sensor, they are very expensive. They are only an oxygen sensor in the generic sense. They are more accurately referred to as a Air/Fuel ratio sensor. And if you get one for less than about $250.00, expect to have problems with it and the fuel management control. If it is the rear, the price you quoted is pretty much in line. BE WARNED— Merely replacing the sensor may not repair the problem. You could have fuel management problems, and the sensor is doing what it is supposed to, and the computer turned the light on to tell you about it. Make certain proper diagnostics are performed. Happy Motoring

There is no primary,there is an air fuel ratio sensor in front of the cat.,and there is an oxygen sensor to monitor catalytic converter performance that is why it is located after the cat.