I'm a newbie to the forum. Looks like its an error for my braking system. this error didn't show up until i replaced my front pads and rotors. they were in bad shape. when i did the work it looked like one of the calipers wasn't allowing one of the pads to slide back when i let off the brake. it's all cleaned up and lubed and stopping perfectly now. I do all my own work. well as much as I can do mechanically with all this computerized emissions stuff.

Oh for the good old days when you could actually sit in an engine compartment. My 1st car had the old slant 6.

 

Welcome to the site. I moved this thread to the first generation Durango section,
FF

 

An off the wall suggestion, but pull the vacuum line going to the brake booster and make sure it's not full of oil. Seriously. I had this happen once on a Blazer that I owned, wore the front pads down REAL low, pushed the pistons back in & replaced everything, and it came up with a Chevy equivilant of the code for a brake booster sensor error. I found that the line going to the booster was filled with oil, cleaned it out & all was fine. What I had done wrong was to push the pistons back in without removing the reservoir cap, somehow oil was drawn up into the booster line.

But hey, it was a Chevy.... anything could have happened!

Bob

 

P0556 Brake Booster Press Sens Circ Range/Perf

Could also be the check valve. Try to replace it. It is the plug that the vacuum line plugs into.