o2 or pre-cat problem...Im Stumped ????

[iluvmymax]

Just bought a 2000 maxima SE with 107k. I love the car. The day I got it the shop instaled a new MAF sensor because the car would cut out in 1st gear. They instaled a updated Maf and the car ran mint. about 200 miles in the SES light goes on. Pulled the code and it says O2 sensor. cleared code ... It comes back after 30 miles of driving. The shop says maybe I need to flash the computer because the MAF is an updated part. OK did that @ the dealer and after 274 miles of driving with no ses light it comes back on!!! The guy at the shop says if it comes back you may have to put in a pre-cat???? How much is a pre-cat? Im stumped and the car has had the ses lioght on sence the firsat day i get the car. car seems strong and runs good. And i have a nother lil problem...... when i start my car sometimes it makes a high pitch whining sound for a second or 2 @ start up. kind of sounds like a cold bearing spinning. it dosent always happen. has anyone else had that problem. I love the car, I just want the car to have no ses light. Any help would be great . Thanks

[blackmax23]

If it's a bad pre-cat, then you have to replace the y-pipe, depending on which bank it is. If it's bank 2, then you will have to replace the whole y-pipe, which can be pretty expensive if you buy it from the dealer. Also, if you just cleared the code and didn't fix/replace the o2 sensor, it'll just keep coming back on until it's fixed.

[iluvmymax]

P0430 - Catalyst System Efficiency Below Threshold (Bank 2)? So should i replace the y pipe then go from there? Where can i get a y pipe and @ what price. The car is still under the 60 day waranty so im not paying for anything. its nice not having to pay $ but i hope this works and clears the light. is there anyway to test the pre-cat before i remove it?

[Sentientbydesign]

Wouldn't it be a good idea to replace the 02 sensor if the CEL came on with a code for the 02 sensor?

Just in case you're not familiar with a pre-cat, it essentially performs the same function as the cat does for the first few minutes when the exhaust is still cold. Once the exhaust temperature gets high enough, the cat can begin working.

[blackmax23]

Well, now with that catalyst inefficiency, it doesn't sound much like the o2 sensor being the culprit. As long as you're not paying for it, just get an oem one from a dealership. They'll reflash your ecu as well and that should do it. These huge pre-cats that maxima's are notorious for having are nothing but troublesome and they rob so much hp and torque it makes me sick!