Beb & SMD are right, I've just had a look through the 350z manual and the module that he refers to is the "unified meter and Ac Amp", the unified meter is the speedo and tacho binnacle, apparently you need to get the car hooked up to a consult II diagnostic reader for the fault code, it sounds like your module might be faulty, although I think there maybe some fuses involved too. This might help:-
viewtopic.php?f=10&t=62619&p=898703&hilit=350z+manual#p898703
+ 1 I believe I would check the connection to it and the ribbon too