HELP VTM-4 lock LIGHT COMES ON my MDX
 

CAN someone please tell me what the he-- the vtm-4 lock light keeps coming on the dash without hitting the button.car is running great no other lights on.seems like when you start the car no light is on till you drive about 20 miles ,then the vtm-4 lock light comes on. car has about 70,000 miles on it.could it be the differental fluid needs changed? i really don't know if this fluid ever been changed.talked to some people ,and they told me it could be the tranny or rear end.please any input.thank you in advance.