Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 11, 2025 ...

The dryer need the desiccant filter replaced annually

The issue has shown itself when I engage the parking brake and white dust blows up like smoke.

White dust blows up like smoke from where, exactly?

Are you saying that white dust blows out from under the dash in front of the driver seat?  If that is the case, then you do have a major problem.  The PP-1 parking brake valve is practically at the end of the air system farthest from the air dryer.

Please give us more details about the symptoms you are observing.

IMO, that may be a bit excessive. Every three years is the common recommendation unless you drive a LOT of miles or operate in very humid conditions most of the time.

OP, suggest you do not start the engine until you verify whether there is any desiccant in the wet tank.  Operating the coach can continue to spread the desiccant throughout the air system.

Yes, from under the dash.
The dust when parking brake is engaged has been the only symptom I have noticed.

I should have said potential major problem.  In order for desiccant powder to migrate as far as the parking brake valve it must have traveled through several valves, check valves, air tanks, and air lines.  If you haven't noticed any other strange symptoms from your air system, you may luck out.  Sometimes most of the errant powder will settle out in the bottom of the air tanks, perhaps mix with a little moisture into a paste, and cause few problems.

You can do a search on the Forum for posts dealing with desiccant contamination of the air system and ways other members have dealt with the problem.  I listed a couple threads below to get you started:

Desiccant powder in air system - anybody else with this experience?

2003 U320 - Phase 2 of Desiccant Powder Cleanup Complete