What should a driver do if a MR leak is detected on a DM car?

When a main reservoir (MR) leak is detected on a DM (Diesel Multiple Unit) car, closing the MR end cocks at both ends of the affected car is a crucial and immediate action. This step serves to isolate the affected car from the rest of the train's pneumatic system, helping to prevent further loss of air pressure which could impact the braking and functioning of the entire train. By sealing off the leak, the driver ensures that the car can be safely removed from service without jeopardizing the operation of the other cars or the train as a whole.

This approach is part of standard safety protocols to manage leaks efficiently and maintain operational safety. It allows for a quick mitigation of the issue while enabling the train to continue operating under reduced risk. The subsequent steps would generally involve notifying maintenance, checking for similar leaks on other cars, and planning for necessary repairs, but immediate containment through closing the MR end cocks is the first and most critical action to take.