What action does the Write mode of the Brake Pipe perform?

The Write mode of the Brake Pipe is designed to generate a brake pipe pressure based on the brake command received from the control system. This means that when the train's control system signals a braking action, the Write mode actively creates and regulates the necessary pressure within the brake pipe to initiate braking. This action is crucial for ensuring that the brakes engage properly to control the train's speed or bring it to a stop, thereby facilitating safe and effective braking as per the driver's commands.

The other options do not accurately describe the Write mode. Reading the current brake pressure is indicative of a monitoring function rather than an active generation of pressure. Pumping air into the brake system would be a function associated with a different mode focused on charging or maintaining pressure rather than responding to a command. Isolating the brake coupler pertains to ensuring that the brake system is disconnected in certain circumstances and does not relate to how the brake pipe pressure is generated based on commands.