Hi Michael, I think it is virtually impossible to over fill the additive tank so ruled that fault out. Tank was half full anyway. I kept loosing Com's with the additive ecu which prompted me to check connections I did get Com's after disconnecting and re-connecting the 12 pin connector but suddenly lost them again, having checked the connector and knowing all was OK I went ahead and replaced the ECU. Nice easy repair for one of these and very little configuring too.

Keith