DIAGNOSIS Contamination inside the trigger switch assembly or a failing return spring. Dust and debris are the most common cause.
FIX Clean externally. Remove battery. Use contact cleaner with a thin straw nozzle. Spray into the gaps around the trigger while working it back and forth. Allow to dry completely. Do not use lubricating oils.
IF THAT DIDN'T WORK The switch mechanism itself is damaged. The 2904 uses a sealed electronic switch module. If cleaning fails, the entire trigger/switch assembly must be replaced as a unit. It is not field-repairable.
HEADS UP A sticking trigger is a serious safety hazard. Do not use the tool until this is resolved. If the tool runs on, immediately remove the battery to prevent injury or damage.