Old fart airmanship. Rule #1. If something electrical does not work check CB's. I did not know AB's do that for you, but then again, system checking sensors can also fail. Sometimes designers can make life more complicated than necessary. I thought there was a cry that modern automatics had encouraged a reduced thinking and less alert pilot. CB checkers? Really. How more thinking dilution do you need? I can understand it when some CB's are inaccessible in the external E&E bay (does an AB have one?), but 2' from your ear'ol?