Recent plugged SCR with about 20K miles, actually a Turbo issue, SCR plugged solid. Comment was there was a potato in the exhaust pipe. Bus would start and stall within seconds, turbo failure, plugged exhaust. Fix was to REPLACE the Cummins Turbo (Warranty), take off the SCR Exhaust, blow the Cat clean, run a regen and retest the engine. Simple fix.