Hello

I have a 1998 Nissan Maxima (SE, I think) with 118k miles. I'm the
second owner....

How often should the plugs be replaced? I believe the existing plugs
are originals...I live in Maine (subject to cold weather...). Are the
NGK cold plugs worth installing?

My Service Engine light is on. The ODBII codes are as follows: P0325,
P0440 and P01448 obtained from Auto Zone. They tell me that the P0325
is the Knock Sensor, P0325 EVAP Leak and P01448 Faulty EVAP Check Valve.

My dealership tolled me that they wouldn't be able to diagnose the
codes until they "have it on the table...and do exploratory
surgery"...another words big $$$$$ sucked out of my pocket...

Knock Sensor...Is it possible that this is due to another problem? I
don't want to be replacing parts if it is not necessary. Someone told
me that the O2 sensors could be triggering the knock sensor....whats
your thoughts on this? Others have said that if the 02 sensors were
bad they would throw a CEL at the ECU, which they haven't at this
time. Could the EVAP problem be causing the knock sensor to trigger?

Auto Zone tolled me that the EVAP ECU CELS are most likely related.
I'm not a mechanic and have very little experience tinkering with our
vehicles. Can this repair/replacement (EVAP check valve) be done by
someone with my lack of experience or should I seek professional help?

Lastly, I also have a bad passenger side, side Air Bag per the
Dealership. Air Bag light is flashing. Dealership says the fix to this
is ~ $500 to $600 of which I do not have at this time . I know that
this is a safety feature but am willing to live with the risk of not
having this air bag. Is there anyway to disable the Air Bag
light...stop it flashing?

Your insight, knowledge, recoomendations would be much appreciated....

Scott