I have a 2010 Grand Caravan - I had just replaced all brakes; rotors; pads & master cylinder - but I am having the same issue as I originally had and that is when I apply my brake it doesn't feel 'solid' it doesn't seem to stop quite properly. I have to push a little extra hard and when I do it doesn't stop as it should it feels like a spring is being stretched - and it is hard. Now my RED BRAKE LIGHT comes on when I do this. I know something is wrong.
One guy searched for codes and got the brake booster performance code COO21 brake booster performance.
I understand it could be the booster; sensor; valve
Any ideas?
Thanks

 

When was the last time you replaced your brake fluid. Brake fluid is sucking in moisture even through rubber hoses 24/7. In my lab I test various materials for permiation of things such as water and even polyethylene (the very best under pressure) eventually lets some water through.
You should change your brake fluid every 2 years. It's a 10 minute, 2 man job.

If you kept up on your brake fluid then the next thing to do is check for a vacuum leak. You can use a smoke bomb, or light powder (baby powder or foot odor powder, maybe flour) to check for air being sucked in to a hose/fitting under vacuum.

 

Sound like vacuum leak on the brake booster.

 

I re-read the original post. Did you bleed the air at all 4 corners one by one?