I have a 2000 Maxima with 98K miles. The SES light has lit three times
within the last month.  A code puller indicated P1320, no other codes.
Since it was close to the time to replace the plugs, I replaced them.
The old plugs looked good.  A week or so later the SES light comes on
again, once again the code puller read a single P1320.  I reset the
codes and continued driving.  Last week the SES light comes on again,
this time with TWO P1320 codes.  I then used the procedure outlined in
a Haynes manual to check each of the coils (resistance check across
two of the coil leads using alternating polarities) and all coils
check out just fine.

At around 60K miles the SES light came on with a P1320 AND a P0302.
At that time I replaced the coil on #2 cylinder.

My question is:

Does the lack of a second code that would indicate a particular
cylinder's coil failure mean that there is some other ignition
component failing?  Or can I still have a bad coil?  Is there some
'deeper' level of codes that only a dealer / repair shop can access
that gives more data about the failure?

Thanks for any help.

Rob