1998 grand am code po 420

i have a 1998 grand am with a 2.4 lit motor. i scanned it the other day and came up with a code po420. wht exactly is that code. how do i get it corrected. was told that it could be an ogygen sensor. they said the up stream o2 sensor. can u tell me which one that is.i can only find one and thats on the exhaust manifold with a single purple wire. wht do they mean by up stream and down stream. im like really confused. any help woukd be greatly apreciated.

it could be your catalyser too that is gone.

The real code is: P0420: Catalyst System Efficiency Bellow Threshold (Bank 1)

it use both oxygen sensor from before and after the catalyser. So it could be the sensor, but there is also code for bad O2 sensors, so... I'ld be more worried about the catalyser...

It could also be the rear (after the catalyser) O2 sensor that is shot.
Could also be leak, plugged catalyser, damaged pipe, damaged sensor/connector/wiring.

thnks for the help. is there anyway to check out the catalic and see if thats really the problem?

Not that I know of, there might be, but the best test is an emission test...

Symptoms-
DTC P0420 - The ODB II system is the test!
The catalytic converter will run cooler.
Any muffler shop can do a back pressure test!

Application:
Up-stream sensor (located before catalytic converter


http://www.autozone.com/autozone/parts/Bosch-Oxygen-Sensor/1998-Pontiac-Grand-Am/_/N-jacwxZ8gcvp?counter=0&filterByKeyWord=02+sensor&fromString=search&itemIdentifier=4966_0_5320_97999

How many miles are on your car? Oxygen sensors should be changed every 100,000 miles. I would just change both the up and downstream sensors and call it good. Unless you're getting a rotten egg smell then i'd change the catalytic converter as well. I had the same code and come to find out when the muffler shop cut and welded a new cat in they didn't weld completely around the pipe and it was sucking air. I bought a magnaflow direct bolt in cat and installed it myself for half the price and the car runs excellent.

I have the same code in my 1999 Grand Am, I got it to go out for a few weeks when I fixed a vacuum leak where the grommet for the PCV plastic line fits into the top of the plenum, it was worn and sucking air. It also threw the same code when one of the plugs was miss firing as well. At this point I do think that it is the second O2 sensor behond the cat converter as that is 233,000 miles old and never been replaced!
:2cents: