i am getting a code for a(n) o2 sensor, where is it,(are they),and after i pull (it)them out is there a way to test if they are good?
They are tested as the car runs. It needs to be warmed up. If they are working fine, they should be putting out about 4.5V as you test it with a multimeter. On a three-wire system, one wire sends signal to the computer, and the other two are for the O2 pre-heater. You may need a wire diagram to determine the signal wire.
In a 99 model year car you should have OBDII or OBDIII emissions equipment, which the o2 sensor is part of. There are usually 2 sensors, 1 in the exhaust manifold/header before the catalytic converter (on the exhaust pipe) and another after the catalytic converter to check a/f mixture after the converter cleans it. You want the engine to be warm to touch but not HOT when you pull it. You need a special adapter to pull it, like a spark plug adapter with a slot down the side to prevent damage to the wires. Exhaust components are often stuck together well due to the heat/cooling cycles they go through. Have the new one on hand when you pull it (about 100-200$) and the code should tell you which sensor it is, read your scanner manual. You will also want to put a little high-temperature anti-seize compound on the new ones thread before inserting it, so you can remove it more easily if you need to.
This article will answer many of your questions about oxygen sensors: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528003cdc5
If the car has over 100k miles on it, you are probably time and money ahead to just pull both sensors and chuck them. I would go with a Bosch or a Denso sensor. Front costs $20 and rear costs $60 on line. You can spend even less if you buy ‘generic’ (one size fits many) sensors and re-use your old connectors. Just be sure to get the appropriate generic sensors.
On all my cars, a regular combination wrench works better than a special oxygen sensor tool. I have the special socket and have never used it.
To truly test the condition of an oxygen sensor, you need an oscilloscope. An old sensor may put out the appropriate voltage but still be responding too slowly to do its job well.