Hiya Ian, I have had same problems with EAM not comming with the host, this means that the big grey box is not connected to the computer. Try disconnecting the cable at the EAM and re connecting and do the same at the rear panel of the computer. You can also restart the computer, with the tiny little reset button on the front panel, left hand side at the bottom, this sometimes clears the fault. As for the O2 sensor, I don't understand the 3.5 mv? From the sound of it, Crypton suspect that the sensor is your problem, as they have replaced it for you,perhaps they have had a faulty batch? Especially as they are 4 years old!! My local engineer told me to unwrap the thing and let it reach room temp before screwing it in, I don't know why, but he does know what he is on about! Usually, anyway!! Failing all else, a chat with Glenn would be well worth your while!! Good Luck, Best Wishes, Gwyn