Sounds like they should have gotten the "more experienced guy" to work on it in the first place. It's hard to find a good technician these days who has the experience and who will take the time to follow the diagnostic procedures to correctly diagnose and repair the problem. A lot of the reason for that is they way the dealerships treat them and how the vehicle manfacturers screw them over on warranty labor rates. Many, including myself, finally say the heck with it and move on to something better.
Anyway, you have two codes that are more than likely related; the one that needs to be concentrated on is the P1448:
On Board Diagnosis Logic:
Malfunction is detected when EVAP canister vent control valve remains opened under specified driving conditions.
Possible Cause:
EVAP canister vent control valve
EVAP control system pressure sensor and circuit
Blocked rubber tube to EVAP canister vent control valve
Water separator
EVAP canister is saturated with water.
Vacuum cut valve
Just because you unplug the EVAP pressure sensor and it set a code and the code went away when you plugged it back in does not necessarily confirm it as "good." It's probably not the problem, but that's not the way to test it.
The problem for you is that you likely don't have the equipment to diagnose it yourself. For starters, you would need a Consult II scan tool (about $3000) or compatable generic scan tool and a vacuum/pressure pump with an adapter for the EVAP system test port (in the engine compartment....vacuum hose with a green plastic cap on a test fitting). These would be needed to perform the service manual tests. If you want, I can send you the test procedures if you e-mail me at
smj999smj@hotmail.com and put "RE: 01 Path P1448 test procedure" in the subject line. Another way that one could test for the leak is with a smoke machine. Most GM dealers have these as they were forced ship to them; a well-equipped Nissan dealer MAY have one. The smoke is an inert gas that is pumped into the service port and will exit at any leaks in the system; this is another tool that runs in the thousands of dollars.
It could be that the vacuum cut valve is faulty. This is a plastic valve with four vacuum hoses going to it, located under the rear of the vehicle not far from the coil spring and spare tire. Two of the hoses go the the vacuum cut valve bypass valve, with is an electric/vacuum solenoid switch that sits just below the VCV. The electric solenoid of the VCV bypass valve has also been known to stick at times and be problematic. I'm not suggesting you replace these items, just letting you know that are possible problems that would need to be confirmed bad and could cause your code. It's also possible that the gas cap valve is faulty (valve is designed to maintain 0.5 psi in the fuel tank) or the fuel sender "O" seal is leaking...not common but I did encounter it on an Xterra, once.
A Nissan or Infiniti dealer would likely be the best place to find someone that can fix your problem and has the equipment to do so; whether that person be at your current dealer, I can't say. You may want to contact Nissan's customer service hotline ( 1-800-NISSAN-1 ) for assistance. Perhaps they can get a Nissan service rep to assist you.
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