A 2004 diesel must be compliant with EOBD rules. So any cheap EOBD/OBD2 scanner should work.
Are you sure it's a 2004 and not a 2003 model?
If it is a 2004 model then you have a problem in the car. Wiring between diagnostic connector and ecu or a defective ecu.
Which pins are present in the diagnostic connector?