So my battery went to zero following a faulty control module for the PDC. Battery now sorted but trunk lid does not power open / close. Is there a procedure to follow after the vehicle has lost all power for a while like with the windows and sunroof to get all the limit points set for the trunk lid?

All wires have fine continuity to the mechanism and the controller. Trunk buttons illuminate and the power close locks the doors but that's all. The trunk close button does nothing at all. Trunk lock / unlock latch works fine. All fuses are fine - is there a relay that needs checking?

I pulled the controller out (A2118703026) and AFAIK there is no way to test this unit other than running it in the car.

Any ideas?

Wires may have fine continuity but verify wires are not shorted to chassis. This one bit me in the butt for almost $500 once... lesson learned.

This wire is located in the left trunk hinge. And I believe the wire is brown, if my memory serves me.
I had this wire snap in half, as the car ages these wires become brittle and eventually break, as they flex from opening and closing of the trunk.
This could be your problem as well.

I think I had to do the same as when you hold the buttons down for the windows and sunroof to reset them by pushing down or holding up the button in the drivers door for 2 or 3 seconds. Really I forget but I do remember checking the wires and all that because of it and it up being some sequence of button pushing that brought it back to life.

Well I had my battery disconnected for a while and obviously had the trunk open. When I reconnected the battery I had to do nothing at all for the power trunk to work. It just worked.

Ah, the joys of distributed digital controls!

To add to this thread, check the manual release lever located over the license plate! This past weekend the trunk closure mechanism malfunctioned several times. Trunk lid would close then pop open, would close halfway then pop open, would get stuck in the half open position and I would have to push it shut manually. I was getting ready to dig into the harness when I happened to glance at the manual release lever over the license plate and realized it was stuck in the open position. Popped it loose with my fingertips and all is good. So, start with the simple stuff!

Good Advice

Well I am stumped.

Fuse by the battery - > Fine (F88)
Fuse by navi block - > Fine (F011)
Connections from trunk lid to controller - > Fine
Connections from fuse block to controller - > Fine
No breaks in any wires from trunk lid to main harness.

Next Ill check power to trunk controller - really last option now but how this is not getting power I don't know. Perhaps the open / close sensor unit is faulty?

What I don't get is I must have disturbed something when I replaced the parking sensor controller as all was working fine before I did this.

Could this have messed up STAR recognition of the auto trunk controller? I know when I got the battery and all else sorted everything required resetting (window / sunroof limits), COMMAND had also flipped to German - not seen that happen before.

Battery disconnect / reconnect after 10mins did not change anything.

Any way to test the damn controller out of the car?

All kinds of gremlins can show up when a battery is low. Between the beginnig of being low (a little below 12 volts) to totally drained there is a enough time for all those gremlins to show up. Just as COMAND converted to German, your car may well have changed things with the trunk closer. It may have even set it to 'Not Present'. Do you have Star? If so, go in and see what you have for the TLC - Trunk Lid Controller. If it is shown as present then go to Actuations and activate both opening and closing.