Engine light on, Engine suddenly louder, reduced power

2001 ZD30Tdi 154hp. Unmodified. Driving with no problems the engine suddenly sounded louder.....crackly and harsh. Engine light came on and went into reduced power mode. Switched engine off restarted but still sounds like an old bus and light comes back on within seconds. No smoke. If I switch off and restart light goes out and full power returns but engine still sounds harsh.....light soon comes back on and goes into low power mode. Plugged in scanner but will not connect. So far I have replace air and fuel filter, replaced mafs, replaced egr and cleaned whole egr system. Fault still persists no change. Any ideas?