15 amp. Breaker trips immediately upon setting. Circuit consists of 4 Outlets, 1 Fan,and an outside front porch light. Checked all components. Don't read short to gnd or Ntr unless meter is set to M Ohms.How do you check breaker?

Using an Ohm setting and measuring power will blow the meter. How did you check the components? If the breaker instantly trips, you have a short.

Is the breaker a standard 15 amp or is it a GFCI or AFCI breaker? I would suggest unplugging everything on that circuit and turning the light and fan off, and then trying the breaker. Have you replaced or added anything new recently? Try taking the hot wire off the 15 amp breaker, and see if it trips by itself with no wire attached.(if you know how to do this carefully so as not to get hurt). If it is an AFCI or GFCI breaker, it could be the breaker, but generally not.