During the last coupla months, the repair shop has run out of options in the supply chain to replace the unit with a new one, or another 'rebuilt' one. The owner settled up for the diagnostic effort and the battery was dead (due to sitting for so long)....
At this point they will take the truck back to their business - with no warning buzzer but a icon on the dash indicating 'brake'.
The pedal response is excellent in all the test modes, and to recap the story: the mechanic's test instrument reports a bad pressure sensor in the unit - but no individual repair parts are authorized or available. This explains the warning light. Indeed, one can postulate if another problem manifests, then how to determine - etc etc.
The truck owner will likely commission one of their staff to commence a search high and low for a unit. Wrecking yard may be the last resort - yikes. My intitial searches using google showed two places listing the item, but it was backordered in both website locations.
The Ford OEM situation for these trucks designates only certain dealer locations as a commercial truck center and one of the closest is 150 miles away. The repair shop contacted the place by phone and email and got no response, followup yielded nothing and then one new worker to the parts place thought the system indicated the OEM parts book (their data base) had a code for the part ~ which meant obsoleted. Possibly it is as simple as a new number replace it, but that is a hopeful wish.
Summary: cost of three or four replacement events with this part and the rental cost, has exceeded the amount they paid initially for this truck out of the Leasing Company fleet. Granted inflation alters this calculation and there has been a lot of that lately.
The usual big place (wholesale upstream) that rebuilds these items dropped this product line entirely cause they were repairing them and tested them sat but they wouldnt last the one year warranty period and they couldnt get reimbused from Wabco - so they didnt renew their contract for the rebuilder task.
The only rock left to lift is the one where they can find a replacement part.
2015 Ford F650 Brake Hydraulic Compact Unit with ECU. (Looks like a big block of aluminum with two pressure domes and some gizmo's attached to the surface of the block).
At first glance the contrivance seems like a novel idea - ABS, contingency brake hydraulic power, power boost etc etc all in the unit and out of the engine compartment....then realization occurs.
Not happy posting all this sordid news on the forum - like it a lot better where we can all review a Solution.