Thank you for your in depth response. I do however, have a number of questions, and would greatly appreciate your input.
Just to confirm I have the dpf with the additive tank.
Is the software programmed to continuously attempt a regeneration if the cycle fails? I would think that it would stop attempting to regenerate after x attempts, and just give PCM alarm "regeneration period"?
I had a fault a number of months back for the fuel cap filler sensor, but my mechanic just cleared it without investigating. Could this contribute to the problem?
If the cycle is failing because of a sensor/actuator, would that not show on the PCM as a fault? i.e. if the turbo is faulty, would that not show? If the EGR is not stuck or faulty, would this show on the PCM? Same question for glow plugs and all sensors?
I had to replace the rubber tubing on the turbo inlet in August as this had split. The part came with a new MAF. Does this need calibrating? Could this be delivering too much/too little air?
Do I have to replace the dpf to diagnose the problem as the mechanic can't diagnose the problem without the car running?
Can you please list the other sensors that control the regeneration cycle please? temperature sensors etc..