I went to the dealership to buy some filters today, so I sneaked a look at the OVP unit (57 pounds, not too bad). I then looked at mine, and established that the fuse in the top was not blown. Does anyone have any ideas as to how I test the function of the ovp unit?

Something I did notice though, was that the ovp that the chap in the dealership showed me had 2 fuses in the top, mine has just one. Sounds like the updated design that dieselbeagal mentioned.

How to start fault diagnosis?

Thanks all!