Hi Slick... wow - here we all are again LOL... how are you!
I wish I knew the answer to your code 122 - however I have met a guy here who really understands everything about these systems - I have messaged him re: this - lets see what comes back!

Strange this thread should re-appear in my e-mail but only 48 hours ago I stripped down the compressor completely on my 4.8is

It was getting through one of Andy's piston rings about one every six months. So Andy offered me a new Cylinder head for the compressor (very reasonable price) so I grabbed it... Mine looked fine but I needed to eliminate cyl head problems etc...

However it was not without its comedy moments.
Removed compressor as have done before.
Dismantled to the point of changing piston ring - done this a few times - a doddle...

New to me ...
Unbolted 2 long bolts that hold head to black air chamber... large spring pushes them apart... however as they separated, out falls a circular perforated dish & small spring & little valve from one end with tiny little thin washer.... the large rusty spring falls out, then from the other end a plastic round thing (lives on a shaft) a flat round perforated plate, a piece of circular black gauze & here it is......... about a million little beads fall out from the other end, hit my work bench (utility room work surface like a mad explosion of M & M's ... lol) which thankfully was clean....... I did not know whether to laugh or cry!

Unfortunately where the beads exploded unexpectedly they went in every nook & cranny to include crank assy sitting nearby on the table... so once gathered most of the little balls had to air-line every last one out of the unit.... I mean they went everywhere! The large spring was badly rusty so but kit he sent had a new one.

The tiny valve in the top of the head (behind flimsy spring) looked a bit worn.... what does this do & do they ever need replacing? Anyone any ideas?

Anyway... reassembled & re fitted... eventually. On restart compressor kicked in immediately... but shut down after 20secs with a long list of fault codes... 5 or 6 there mentioning probs with high pressure valve & all sorts.... deleted these... it ran for another minute then a code 76. Cleared this one and clean bill of health from then on. Car level up/down control responds fast .. 13 bars pressure or so at the mo... comp seems to run much shorter time which can only be a positive eh!

And on it goes eh!
Malc