On a Cummins ISB common-rail school bus engine, the scan tool shows commanded rail pressure much higher than actual rail pressure at cranking, and the engine will not start. Technician A says excessive injector return (back-leakage) can prevent rail pressure from building. Technician B says a faulty high-pressure pump or rail pressure control valve can prevent it. Who is correct?

1. Technician A only
2. Technician B only
3. Neither A nor B
4. Both A and B