I don't know which one to order. Someone told me that a CA car has 4 o2 sensors. Is this true?

Look in the front of the engine bay and see how may sensors are up there. I believe you can look at the vin to find out too. Even check the y-pipe thats on there now or count the # by getting under the car.

Since you are 99 it is possible that you have the dreded cali y pipe with extra pre cat.

Cali y-pipe was used as early as '95.

Just look at your VIN number, the FAQ will tell you how to decode it and find out if its cali or fed.

Not 100% true, my VIN said I had a Cali spec car, but I only had 2 sensors. Counting the sensors is your best bet. Ask Custom Enterprise for the link on their site that shows you what to look for.

This thread might help too

http://forums.maxima.org/showthread.php?t=451394

Thats news to me.

alright well i do have a cali car so i obviously ordered that spec y-pipe. Can't wait until it gets here, possibly tommorrow or monday

Change your oil

cali spec and fed spec have the same amount of pre cats..

99 Cali spec has an extra precat in one of the exhaust mainfolds. The fed spec does not. Hence why a different y pipe is needed for 99 cali spec.

Now would this code be the pre-cat I have just replaced the cat that is just before the muffler. I have the california emissions exhaust. Gotta clear this up before inspection