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Discussion Starter #1 (Edited)
I've searched "tailgate", "liftgate", "hatch", etc and have seen most problems are with the closer mechanism. Mine appears to be different.

My newly acquired '08 R350 will open the tailgate fine, but it won't close the door - stays wide open. If manually closed, it will pull the last little bit and latch.

The button on the tailgate itself does nothing. When the button on the key fob remote is held, the closer mechanism makes a sound and does something. This makes me think there could be a limit switch that is not sending the signal to indicate tailgate is open.

Ideas?
 

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Sorry, I don't know what could be the reason. I still got the closing problem myself.

Not sure if there is a fuse for this, did you check that?

Also does the problem occur on the driver door button as well as from the tailgate itself?

Good luck!
 

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2008 R350 4MATIC
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mb1x,

Did you ever figure out what was wrong? I have very similar symptoms, where the liftgate opens fine and remains opens at the proper height without any sagging. The issue is trying to close the door. Any method (keyfob, driver door, liftgate button) to close the door results in the chime but absolutely no movement so I have to manually close it.

I believe the issue is whatever actually pulls the liftgate down and not the battery or latching mechanism, which I replaced in the past, but I can't find a good diagram to understand what the pulling force is (hydraulic pump or electric motor). It appears that the strut and spring on each side near the hinges is to assist the pump or motor in opening or closing so the fact that I can have the liftgate remain in the same position halfway open leads me to believe it's none of those. I tried closing it when it was only a few inches open with no luck, so the fact that it wouldn't close with all of the help of gravity making it easier is what finally convinced me the pump or motor just isn't turning on.

It could be a fuse, loose wire, bad motor, etc, but before I ripped the car apart I figured I'd ask to see if it was something completely different.

Anyone else know of a good DIY to get to where the pump or motor is?
 

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1987 560SL - Signal Red, 2014 ML350 - Diamond White, 2019 Ford Explorer - Magnetic (company car)
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It's hydraulic, I might be able to find the diagram, If I can then I'll post it.
 

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2005 C240 silver, 2008 R320CDI Cubanite
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have a look at these . Main components.
My hunch would be the obstruction sensors.

My issue is that the liftgate unlatches, tries to lift, but then relatches. Dealer says its the pneumatic struts that assist the hydraulics.

There are more diagrams available. let me know what you may need
 

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Appreciate the help! I'm traveling now, so I won't have an opportunity to dig into it more for 2 weeks. Anyway, I'll share whatever I find.
 

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2008 R350 4MATIC
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19 September Update:
After installing the new Arnott suspension bag last weekend I decided to revisit the liftgate issue to see if I could learn anything new. I removed the N121/1 controller so that I could crack it open to see the circuit inside and determine if there were any obvious signs of damage. I noticed there are a couple of SPDT relays connected to the hydraulic pump with the powered off state being that both wires are grounded. That being the case, my assumption was that the polarity to the pump should change and my 0V reading was an issue. I briefly connected a 9V battery to the relay coils to listen for a relay click to see if the reversing relay was bad. Both relays seem to work fine.

Thinking the issue was buried deeper in the controller than I had time to investigate last Saturday, I put it back together and reinstalled it in the car so my wife could at least power open the liftgate. For giggles I hit the liftgate button on the key fob just to hear the chime before having to manually close the liftgate, and lo and behold the liftgate closed by power. No clue what actually fixed it, but I don't think it's simply related to recycling power to the microcontroller within the N121 controller as I very recently replaced the battery. Maybe just a stuck relay that needed a little gentle persuasion.


7 September post:
After knocking out new tires, brakes and looking into the auto-leveling suspension issue on our R350, I finally got a chance to investigate this liftgate issue a little further.

With the liftgate closed and the 4-pin connector to M51/1 (hydraulic pump) and Y102 (automatic closing control valve) connected, I read +12V from RDBU to GY wires going to M51/1 and 0V going to Y102 and the liftgate opens fine.

With the liftgate open and the 4-pin connector disconnected, I read 12V going to Y102 and 0V going to M51/1 when I attempt to close the liftgate. The RearHatch electrical 2 drawing doesn't identify a set polarity on the M51/1 RDBU and GY wires like it does for the Y102 wires, which would lead me to believe the hydraulic pump runs forward and reverse by switching polarity. Should I be reading -12V from RDBU to GY wires going to M51/1 when closing? If so, the 0V on M51/1 may be due to a faulty input obstruction sensor into the N121/1 controller, but I would think the controller would also inhibit the voltage to the Y102. I guess it could also be that the obstruction sensors are fine and there is a hardware issue inside the N121/1 controller. If someone can confirm that I should be reading -12V from RDBU to GY, then I'll investigate the obstruction sensors and controller further. Does anyone know how the sensors work so that I can bypass their inputs into the controller? If they have a nominal resistance value, I could replace them with fixed resistors into the controller. For the controller, I imagine there are relays or power transistors on the board which I could potentially read part numbers.

Anyway, with the liftgate open and the 4-pin connector connected, I see 0V going to M51/1 and a small blip in voltage going to Y102 and then nothing else. If the closing control valve is the only component involved in the closing operation, it would appear there is an issue with it. Is the Hoerbiger closing control valve (p/n HB70368-016D) in the Mercedes A 251 800 04 48 pump assembly a replaceable component? Would removing it from the aluminum block to isolate it from the rest of the system release a sea of hydraulic fluid or is it a dry interface within the block? I fear I know the answer, but figured it didn't hurt to ask.

Okay, now to turn my attention back to the auto-leveling issue and order the Arnott rear air springs. Thanks again guys!
 
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