Started off with brake booster, I patched it up but it kept throwing the alarm every time I started so I investigated a few times. Then 4 wheel drive system faulty. Meanwhile I changed front pads (reused wear sensors) and got another brake warning. TPS low tire pressure. It got so that every time I turned it on it was a parade of alerts.

Finally got time to change out the brake booster hose, also replaced coolant expansion tank since it was in the way. front pad sensors, air in the tires and all the codes are gone!
The 4 wheel drive system faulty I now suspect was because the brake booster pump was kicking on so much it must have caused a power dip to some component that supported the 4 wheel drive system.

Been driving for a week with no codes and it is wonderful! Love this car. Now for the worn tires. . .

 

Congratulations! I too hope to be code-free at some point in the near future.

 

Don't forget the battery!

 

Code-free on a 955 is a moving target for sure. At one particular low point soon after purchasing I had the brake booster faulty, 4-wheel drive faulty, psm off, airbag fault, break service, coolant low, and to add insult to injury, low fuel. All the while the blower fan was squealing.
I was half way out of the neighborhood before it stopped buzzing at me.

No feeling quite like starting it up and having 0 warnings!

 

I spoke too soon!

4 wheel drive system faulty came back. rats! brake booster vac pump must have had nothing to do with it.

While in drive I tried to engage 4wd and it only blinked. no error. So following a previous post I went in reverse and slid in neutral. pop.
Then in drive I again tried to engage 4wd and got the idiot warning that you must be in park. great-its active!
Then put in park, brake on and cycled through 4wd down the street so I hoped exercising that would keep the bad spirits away. no dice. still coming back. Looks like I will need to order a 955-624-601-01. Just hit 75K miles. . .