DPF forced regeneration may not be possible if fault codes 1901 (general DPF code) and 2003 (specific overpressure code) exist together.
The presence of these codes indicates that the DPF is becoming blocked and creating high pressure pre DPF. Initially this will not have obvious driveability issues but over time driveability will degrade as the DPF becomes clogged.
Forced regeneration is not possible in this scenario as a safety measure to prevent possible thermal related failures from happening during the DPF regeneration process to both engine and vehicle systems.
The most likely cause of these codes occurring simultaneously is due to the drive cycle which the vehicle undergoes. This is most likely to be repetitive short journeys where the exhaust temperature does not achieve the desired temperature when normal regeneration should occur. Typically regeneration should take place between 300km and 1000 km in service depending on drive cycle.
The repair procedure is to replace the DPF unit.
However the vehicle must be referred to Vauxhall to have the latest software uploaded into the control module which should enable the driver to see if the regeneration cycle has not been performed by indicating a flashing glow plug lamp.
Always ensure that the turbocharger, fuel system and engine oil are in good order when replacing DPF units, as any one of these elements can cause premature failure of the DPF due to high emissions rates as a result of malfunction.