P0556 Code

[Navigator55]

Looking for help on a P0556 code (Brake Booster Pressure Sensor Circuit Range/Performance). It comes with a "Check Brake System" warning on the dash. It doesn't come on during my daily 20 min drive to work; but has come on the last four times I've been on the interstate. It's been pretty consistent in that it comes on ~10 min after getting on the interstate doing ~65mph. No issues with the brakes and they work the same after I get the warning. Once I turn the truck off, the warning goes away until the next time I'm on the interstate.

One other thing I've noticed. I had my Cam Phasers done about 2 months ago. Ever since, the brake pedal is a rock when the truck isn't running. Once the truck is started it feels normal. I didn't think anything of it until I started getting the warning messages.

I'm thinking a bad sensor or maybe a vacuum leak? The vacuum leak seems to make sense in that when the truck isn't running or making pressure the brake pedal is hard. Any ideas where to start trouble shooting?

Truck is a 2019 with ~42k miles on it.

 

[Navigator55]

Update. Figured out I was getting this warning if I didn't press the brakes over a certain period of time. Drive to work is 20 min on city streets with traffic, stop lights and stop signs. Light never comes one. The interstate driving is later at night with minimal traffic and check brake system warning flashes after ~10 min. On one of the trips, I tried touching the brakes every min or so and no caution light. After doing some further research, I tried replacing the Vacuum Tube (JL3Z-2420-AA). It was an easy remove/replace so figured I try it before taking to the dealer. It's been a week, 4 interstate trips and no light so far. The pedal also feels normal now when pressing to start the truck. So it appears I had a leak somewhere along that vacuum tube assembly.

Here is the JL3Z-2420-AA.

 

[Lane2018]

Sounds like you may have it whipped. Unusual problem it seems, glad you shared!

 

[SCAR911]

Awesome. Thanks for telling us the fix and part number. I'm sure it will help many others in the future.

 

[BadluckRaptorguy]

Update. Figured out I was getting this warning if I didn't press the brakes over a certain period of time. Drive to work is 20 min on city streets with traffic, stop lights and stop signs. Light never comes one. The interstate driving is later at night with minimal traffic and check brake system warning flashes after ~10 min. On one of the trips, I tried touching the brakes every min or so and no caution light. After doing some further research, I tried replacing the Vacuum Tube (JL3Z-2420-AA). It was an easy remove/replace so figured I try it before taking to the dealer. It's been a week, 4 interstate trips and no light so far. The pedal also feels normal now when pressing to start the truck. So it appears I had a leak somewhere along that vacuum tube assembly.

Here is the JL3Z-2420-AA.
View attachment 444288

I'm having this same issue. Service brake system comes on when I go on longer drives. I might give this a try.