The panoramic sunroof stopped working on my 2013 W204/C204 C63 Coupe during the hot weather a couple of weeks ago. It never showed any sign of failing, it just suddenly refused to open one day and there was just a faint click from the motor unit when you tried to open it. Interestingly the sunblind continued to work just fine. The W204/C204/C207 have two motors in the roof, one on the left which is the one that drives the sunroof, and one on the right which drives the interior sunblind. Since the sunblind was still working, I thought it might be a switch fault so I bought a new over head panel which was easy to replace but still the same thing persisted, so this pointed to the motor. Strangely, when I started merely touching/fiddling with the main sunroof motor, the sunblind started intermittently working then completely stopped too. I read the codes on Mercedes for Carly and it stated "984971 the actuator motor roof system has a malfunction. The actuator is blocked". I could use the manual opening and close allen bolt on the motor to open the roof so couldn't understand why it was saying it was blocked.
Anyway, Mercedes wanted £450 for a new motor unit which I wasn't going to pay, so I got a second hand one off eBay (part number A2128200308 - it is also the same motor they use in the E Class Coupe C207). For some reason only known to Mercedes there are three different part numbers on the motor unit (you wouldn't get this on a BMW!!) but the above is the correct part. There are several revisions of the motorunit, but nothing that'll affect the compatibility) for £30. I had to remove the overhead interior light panel (easy to do - just stick a credit card at the rear most part of the panel and wiggle it a bit and it'll drop down) and you can access two of the screws to the motor unit (Torx T25) but a third is not accessible due to the headlining. So I had to drop the headlining at the front by removing the rear view mirror and the rear view mirror mount (3 x Torx T20), the front grab handles and driver/passenger sun blinds which were easy to get off. Then I had enough space to get a small screwdriver in to get the third screw out for the sunroof motor and it just easily comes out. The first time doing this took me about 1hr. The second time, when I timed myself, I did it in 12 minutes. Having those plastic interior trim removal tools is a must.
I initially tried to just put the complete new motor unit in the roof started partially working again, but would open an close an inch at a time and I would get the error message "984951 the actuator motor roof system has a malfunction. The component is not programmed". Unfortunately, it needed coding to the car with a Mercedes STAR system which a local Merc independent kindly offered to do for £100 (eff off!). So my work around for this was that the "motor unit" comes in two easily separable parts - the physical motor, and the electronic PCB (see pictures below). The bits with all the programming etc on was the PCB part with all the chips on, and I just used my old PCB unit and clipped it into the new motor part and hey presto - it worked and as the car still recognised the PCB part as the part that came from the factory - no coding necessary and it works perfectly now. To "recalibrate" the roof, you simply hold the button for a second or two after closing the roof and you'll hear the motor make a very brief noise and it's done - none of this rubbish about holding it for 10 seconds one way, then 10 seconds the other way etc etc etc
Anyway, a long winded post but will hopefully help someone in the future somewhere on the internet. One thing I've discovered owning a Mercedes after owning numerous BMW's is that there is sweet FA information online compared to BMW's. If I had this problem on a BMW there would be 10 DIY guides, with Youtube videos, pictures and full information. For a Mercedes? Absolutely nothing and most of it is on American websites where people haven't got a clue what they're talking about most of the time.
(Rear view mirror mount)
(Rear view mirror - just tilt to one side and pull down to release from the mount. To get it back in, use a screwdriver to put some pressure on the pin as you push it back into the mount)
Reuse your old PCB bit, and use the motor part of the new motor unit and you don't have to worry about recoding anything to the car (assuming the motor part is the bit that's failed and not the PCB. I'd suggest it would be almost always a failed motor over the PCB though)