I have a 96 Sentra GXE. After changing the head gasket, I got a "check engine" light. I went to the local Auto Zone to pull the code and the sales guy read P0340 or Camshaft Position Sensor. I looked in my manual and found out what this is. I would like some suggestions about what might have caused this problem and what I should do next. I should mention that I did fool with the timing a bit after I installed the head. The car runs fine, though the gas mileage maybe just a bit less.