Hi folks,
I've just read this thread...
The lumbar support fuse is located at the base of the left-hand-side A-pillar. You have to remove the sill trim in order to access it.
At the base of the A-pillar, you'll see a whole raft of connector blocks. Piggybacked onto the connector blocks you're likely to find two fuses. One is large (30A, if I remember correctly) and another is small (10A). The smaller one (10A) is the fuse for lumbar support.
Both seats are protected by the same fuse, so if one seat is working and the other isn't, then the fuse is unlikely to be the problem.
The lumbar support system is an electrical island; it is in no way connected to the CCCU nor the car's diagnostics system.
The lumbar support connectors beneath the seats (red) have 6 pins, of which only two are used. There should be ~12V between the red and brown wires irrespective of whether the ignition is on or off.
All the best,
Tom