check tire pressure light on 2006 Nissan Titan

i have a 2006 nissan titan. and the check tire pressure light comes on all the time. the tires are at the correct PSI. someone told me that its because the spare is missing> can anyone plz tell me whats wrong?

Asked by for the 2006 Nissan Titan
Mine did the same and it was because my mud flaps were not aligned correctly. no joking...