Y17DT - cod eroare P0251 - porneste cand are chef

People often ask us for advice regarding problems they are having with the Vauxhall 1.7 Dti Isuzu engine.  Engine codes Y17DT and Y17DTL. We have listed a few common faults here which may be of help:
Engine won't start at all or runs for a while then cuts out intermittently. 90% of the time it is the edu causing this problem. However the crankshaft sensor can also cause exactly the same symptom. The usual reply is 'but there is no diesel coming from injectors so it must be the edu. Wrong. A faulty crank sensor will stop the ecu and edu from working so no fuel flows to injectors. Crank sensor doesn't always set a fault code so can be difficult to diagnose. If in doubt change it - especially if you've had edu repaired or replaced and fault persists. It's located near starter motor and held in with one 10mm bolt.   
An immobiliser fault will cause a non start situation and no diesel from injectors, so again this can be mistaken for an edu fault. So check for proper operation of immobiliser before blaming edu.
The ecu on top of engine (with 2 plugs on it) is vital to engine operation so obviously this can cause a non start or other fault conditions. All the signals from engine sensors, throttle, clutch and brake pedal sensors etc are connected to ecu. You can check operation of most sensors if you have a code reader that can display live data.   
The EDU is not coded to car, but the ECU is - so you cannot just swap it. You need one from an identical car with same equipment and change ecu, chip inside key and transponder around ignition lock as a matched set. Corsa ECU also coded to body computer / instruments.
If you have disconnected the fuel feed pipes to pump during fault finding you will need to bleed air from system. The easiest and fastest way to do this is to tow start the vehicle. It's almost impossible to bleed system using the starter,plus you risk overheating the starter motor.
Update: Fault code P0251.
This code can be caused by a faulty edu - but check this also if you have intermittent starting, running or non-start problems .
If you know the edu is working ok and you still get this code it can be caused by a fault in the electrical supply to the injection control circuits.
Check for blown fuses and or corroded pins in the under bonnet fuse box, especially Maxi fuse 6 (20amp) this feeds pin 30 on both the engine control relay (no 4) and fuel quantity adjuster / spill valve relay (no 6). Don't forget to check fuses in fusebox inside car.