Nissan Repair: 00 Xterra overdrive sensor, autozone, xterra

Question
I have an 00 Xterra with a chronic check-engine light problem.  I took it to the dealer and they said the overdrive sensor was sending a code.  However, the overdrive seems to work perfectly (the button on the auto trans shifter).  The dealer told me that this would cost in the $4000 range to fix !  That seems like a lot for a problem that isn't affecting how the car works.  Making matters worse, I'm about to sell it -- and this check engine light problem really hurts the desirability of an ohterwise perfect car.. Any ideas?

Answer
Mike,

$4K is a bit of a stretch if the overdrive works.  If you would go to Autozone or Checker and have them read the code and email it back to me I will let you know your next step.  This could be as simple as the button or as complex as the transmission computer.  But, that would be something like $1200 bucks and not $4K...  Email me back with the code.