dcbetech

I have a 2000 frontier V6 with check engine light illuminated. I took it the the Nissan dealership and had them do diagnostics on it for $80. The error codes that are present are: P0325(knock sensor malfunction), P0151(Bank 2 pre converter lean failure), and P0131(bank 1 pre-converter lean failure). I was pretty ignorant about how this system works when I first went to the dealership, but have learned a lot since. They told me I had multiple exhaust leaks, including, both manifold gaskets, both converter gaskets, and possibly cracks in both manifolds and converters. Long story short, for them to fix the problem they would have to remove all components, inspect, and possibly replace everything to the tune of $1500. My truck is passed all available warranty coverage. I was stunned, because I have no problems with performance. I took it to an exhaust shop who told me gaskets were'nt leaking, but passenger manifold was cracked. I had them replace it for $350 dollars. Engine light still on. I took it to another shop, who said I needed to go ahead and replace both O2 sensors. He was 99.9% sure this would fix it, saying the O2 failures probably triggered the knock sensor failure also. I had him replace the sensors for $359. Light came right back on after two trips in the truck. I've checked all vacumn hoses, electrical connections, and fuses. Truck runs fine. I can't keep paying these guys for work that doesn't fix the problem, and figure I can't trust the dealer's information. I have to have this fixed to pass emmision inspection. The only thing I've done to this truck besides regular maintenance was to replace spark plugs with bosch platinum tipped plugs. I read somewhere Nissans don't like aftermarket plugs. Could this have been my problem all along. I don't know what to do. Any information or suggestions would be greatly appreciated. Thanks.