Yesterday, on a 14 month old car transport trailer, I wanted to have the §21 made “still fast”. Data: Empty weight approx. 400kg, tandem axle, ZgG 3200kg. As far as everything is good, until the tester pulled the thing onto the brake test bench and then, what is a joke, wanted to test the brake on the run, namely by placing 2 wheels in the test bench and driving backwards with the car. Of course, nothing went. §21 did not work, trailer traffic-insecure since brake on the run without function. Handbrake and ATC function perfectly. Any attempts of the explanation did not arrive. In my opinion, the run-up brake can not work at all with unladen trailer, the damfper in the run-up device has 5KN (500KG), according to H ersteller this is so that in the unladen condition the run-up brake is not required, on the contrary, it could then result in loss of control on the trailer if the 4 wheels block. Therefore the high resistance. The ATC works. The tester says it is wrong, the tester does not have to rule.