S211 Powered Tailgate stops halfway on opening & won't close at all.

[Borris1954]

My 2006 (facelift) S211 E Class Estate has the power lift (option code 890). This has worked great until this last weekend when after a heavy frost the tailgate stopped several times on opening and also on closing. I had hoped this was just some frozen water in the hinges or other bits of the mechanism (after I finally gave it an overdue wash) and the problem would clear as the day warmed up. It didn't! So I did some research and found lots of posts about the hinges partially seizing causing similar issues so today I removed the left and right hinge covers and lubricated the hinges with some graphite oil and also some PTFE lubricant. This seems to have has loosened things up nicely. BUT now on opening the tailgate always stops at around the mid position. Operating the rear handle, pressing the key fob or the internal opening button on the drivers door will raise the tailgate fully. I could just about live with this but a bigger issue is that pressing the button on the tailgate to close it (there is no key fob or internal button for closing) does nothing at all.

I am fortunate to have access to a Star Diagnostic System (SDS) and a scan reveals that there are no fault codes (just a stored event for low voltage at the control module at some point in the past). However, the actual values show the door status as not "Normalised" which sort of makes sense given the symptoms. I can quite believe the stop start behaviour might have mucked up its normalisation. Using SDS to normalise the door doesn't really help me as the process requires that you be able to power close the door from its fully open position which I can't do.

If anyone has seen this before or got any bright ideas I'd be grateful for any advice. It just seems very odd to have no fault codes present with quite a blatant fault unless I am just missing the point on how to normalise the door.

 

[Wearsthefoxhat]

Could you not press the close button and then help the tailgate to fully close. It might then register where it is.

 

[Borris1954]

Thanks for the reply - I did try that but no luck.
The good news is that I think I have now found the issue.
The attached photo shows the potentiometer (B24/16 Trunk Lid/rear end door opening angle recognition sensor) disconnected from the ball on the left side of the right rear hinge and lying in the roof channel. The plastic ball has deteriorated and come off the end of the potentiometer. I will see if I can reattach it but suspect I may need to source another one. Having looked at WIS it looks like I can get it out without removing the roof lining by removing the right hand fixing for the net dog guard.


Will look at it later in the week and update any progress.

 

[Wearsthefoxhat]

That looks likely then, you could possibly move the potentiometer fully one way or tother and see if it normalises on Star. Hopefully you can fix it fairly easily now.

 

[bolidemichael]

I've had a year long saga with mine and the bouncing is resolved after having replaced the potentiometer (I'll need to double check my paperwork), the hydraulic cylinder and also the struts. The struts are getting on for quite an age now and should be replenished. The MB ones were NLA for quite a while but are available again. The ratings for the pattern parts don't differentiate between standard and powered boot lids (so far as I understand the feedback from my indy).

The issue that I have now, is that the boot lid slams intermittently, rather than soft closes.

 

[Wearsthefoxhat]

My soft close is intermittent and something I shall look into very soon.

 

[bolidemichael]

The actual mechanism may require repair or replace. My issue is related (after having replaced the soft close unit and I can provide you with the part numbers etc as required) to the final slowing of the bootlid prior to the soft close being activated.

 

[Borris1954]

This is now resolved.

Re-attaching the ball socket connector proved without removing the potentiometer proved quite a challenge. Whatever clip previously held it in place was completely missing. I think the connector was only held in place by some rust on the potentiometer shaft and some overspray of penetrating oil for the hinges washed that away and it then fell off. I tried the smallest fuel pipe clip I had but that was too big and then in desperation I tried the old cable tie trick which as expected failed completely. Finally I rummaged in one of my "odds and sods boxes" and found a power cable clamp that I remember saving when I dismantled a valve "wireless" around about the time we won the World Cup! But of course the screws were too short so another rummage about to find a couple of longer 8BA screws (hands up if you can remember BA screws and nuts?). The upshot is (as can be seem below) the ball connector is once again securely attached to the potentiometer. The tailgate was then closed manually and fully power opened using the rear tailgate handle control and then powered closed using the close button. This normalises the door. Very happy to advise everything now works again as MB intended. Especially a zero cost repair.

 

[Wearsthefoxhat]

Thanks for updating and a good fix. Those “odds and sods“ boxes always come in handy, I have a few too, (though no longer pentode or triode parts), much to the dismay of shmbo.

perhaps a drop of locktight..

 

[Borris1954]

perhaps a drop of locktight..

Good idea. I'll do that tomorrow. I am leaving the covers off for a few days so I can keep applying lubricant to make sure it gets thoroughly into the hinges,
BTW I think the partially seized hinges may be have been why the control module has been throwing the under voltage event in the event log rather too often. The extra current to operate the tailgate may have been causing sufficient voltage drop to trigger this event much earlier than would normally be the case. I'll have to clear that and see how quickly it comes back (if at all).

 

[bolidemichael]

Great work. The polar opposite of my outlay, to date. More fool me!

 

[bolidemichael]

Can I revive this thread for some more general knowledge on this topic? Does anyone know whether the hydraulic fluid that operates the power close function can be topped up?

 

[Borris1954]

I looked into that very question. Under normal circumstances there should be no loss of fluid unless a leak develops somewhere. I removed the left hand side trim panel and opened up the plastic box the pump lives in but luckily the fluid level in mine was still ok. I found this thread which gives two ways of topping up the fluid.

Adding Fluid to hydraulic tailgate

www.benzworld.org

Personally I would go for the second method but rather than drill a hole in the plastic reservoir I would try and make one with something hot like a small soldering iron tip or even a suitable size nail heated up with a flame of some sort. This would avoid the risk of any plastic fragments getting into the fluid and would make the plastic thicker around the hole to better take the screw to close off the hole. Good luck if you try this. Also I would use some of the fluid I bought to top up the hydraulics on the roof mechanism of my SLK after repairing the front latching cylinder.

 

[bolidemichael]

Thanks. Have fwded info to my indy.