park assist and side assist system

[06-Z71]

We have a new to us 15 yukon xl denali, the rear park sensors are not working, when I use the park assist button, it just flashes rapidly and will not stay on. Tried having it in the on position and not running in reverse with no luck, no noises or buzzing whatsoever, side assist warning comes on also, pulled all fuse panels and nothing is labelled for these systems. Anybody know what I should be chasing down before I take it to a shop? Already have had enough fun changing all 4 magneride shocks and pulled off power step motors for replacement this week!!

 

[tuckerrnr1]

Do the backup lights come on when you put it in reverse?

 

[06-Z71]

Yes when the yukon is running.