Hi Kevin. I could give you chapter and verse on this, as there have been some good posts at the BBA forum by Cyril and Steve (pug gods), addertive is injected into the fuel tank at top up, calculatedby a pre and post top fuel gauge reading swicthed by a fillere flap switch. Normal regen happens on a motorway run (full details at BBA) and a forced regen can be done with dealer kit or Actia Multi diag (other,s possible). Regen is done by altering injection point etc so the filter get,s HOT very HOT Kevin. Ps i,m sure Martin and DaveH know more than they are saying