Stewart, I came across this several times,if the pads are changed without the brake system being de-activated then when it becomes active again the pump has to run for too long to achieve brake pressure,ie. it has to run to push all the pistons back out,it sees this as a fault. When this happens the SBC UNIT is f''''d.The first one i saw had to have the unit replaced which ran onto serious money,about £2000,all the others got a software upgrade and it sorted it. The good news is that there is extended warranty on this job so your dealer should do this for you. HTH,