What should be done if the tractor protection valve leaks with the button out?

If the tractor protection valve is leaking with the button out, it is crucial to reject the vehicle. The tractor protection valve plays a vital role in the proper functioning of the air brake system in commercial vehicles. Its primary purpose is to prevent air from leaking from the trailer when it is disconnected from the tractor. A leak in this valve indicates a failure in the air brake system, which can significantly compromise the safety of the vehicle. If air leaks occur, the braking power can be lost, leading to potential accidents.

Rejecting the vehicle ensures that necessary repairs are made before the vehicle is allowed back on the road, thus maintaining safety standards for all road users. Continuing with the inspection or marking the vehicle for future repair would be inappropriate, as these actions fail to address a serious safety concern immediately. Performing additional tests may seem like a thorough approach, but it does not resolve the immediate danger posed by a leaking valve. Therefore, rejecting the vehicle is the most responsible action in this scenario.