At a glance
What can fail
Some vehicles with an optional Wabco air dryer have check valves installed in the wrong location. If the air brake system develops a leak, the secondary air reservoir can lose pressure and become unable to function.
What the fix does
The air line plumbing will be repositioned to properly isolate the air reservoirs using check valves.
Summarized — see the official notice for exact wording, dates, and contacts.