Service Brake Booster on DIC

[03YukonNH]

I've been having a problem with low brake pedal feel for a while. Brakes have been bled and all fluid is new. I just changed the front pads, rears are newer within a year. So now I have the "service brake booster" message that came on once and I haven't seen it since. What would cause this to come on? There is an electrical solenoid or canister next to the booster and reservoir. I've seen hints that this may cause that message with low pedal feel. What is that called and is there a procedure to replace it?

 

[03YukonNH]

So small update: it turns out the electrical canister is the supplemental brake assist pump or vacuum assist pump that supplies extra vacuum to the brake system. The most recent part number is gm 89058946 but it is discontinued. I've called GMC service and asked what they do to replace it if its broken but they said they've never had to deal with it before. Truck has 273,*** miles on it so I'm sure most of you with these pumps haven't put that many miles on that part. I'm looking for an aftermarket alternative but can't find anything. Might have to go used or try to repair mine if I can take it apart.