Yes, in Michigan, you are required to have an air brake endorsement to drive a commercial vehicle with air brakes. This endorsement is obtained by passing a written knowledge test specifically for air brake systems.

There is no air brake endorsement. If you do not pass the written air brakes test AND complete your road test in a vehicle equipped with air brakes, then you get a restriction which prohibits you from operating an commercial vehicle which is equipped with air brakes. It is possible to have a Class A CDL with an air brake restriction.

There is no air brake endorsement for a CDL, period. If you do not complete the written air brakes test AND do your road test in an air brake equipped vehicle, you receive a restrictionwhich prohibits you from operating a commercial vehicle with air brakes (although it has no impact on air brake equipped vehicles which fall outside the jurisdiction of the FMCSA).

You take the written Air Brakes test, and conduct your road test in a vehicle equipped with air brakes.

When you got your CDL did you take the road test in a air brake equipped vehicle? If you did not then you have to retest to add air brakes. Not the whole test just the air brake portion both written and pre-trip portion of road test.