On mine, the override switch on the dash allows the engine to run for 30 seconds if the red 'Stop Engine' light comes on and the DDEC system pulls power then shuts the engine down. This 30 seconds is to allow you to drive the coach off the roadway. 12.57 volts at the starter is good voltage IF there is adequate current available. Have you tried using the Battery Merge switch on the dash? The procedure for starting my 8V92 is check the coolant level, oil level and fuel supply level, apply parking brake, make sure transmission is in neutral, turn key to on position, wait 6-10 seconds for the yellow "check engine" and red "stop engine" lights to go out, turn key to start for no more than 30 seconds. If it doesn't start wait for starter to cool before trying again. 5 seconds may not be long enough to start an engine that has been sitting for a long time.