Tailgate does not latch by tailgate button

My ML500 2006 having liftgate issue. At first when we close the trunk, it won't close perfectly, then, when we use hand to touch the latch (to open the trunk) then we hear the sound noise and the gate closed, Or if we leave the trunk as is then when we started the engine and drive it display the message "gate open" (or something like this) then about few minutes, you would hear the sound/noise from the trunk and it is closed.
Then just last week, when open and close the trunk we heard the noise from the motor keep running non-stop! I drove the car to the auto repair shop and the technician helped to open the panel and remove the wire so it stops making noise.
I ordered a new liftgate actuator from Amazon and the technician helped to replace the all one. Then I could close the trunk perfectly for the first time, then when I open and close the trunk the 2nd time, I do not hear the sound of trunk closing. At this time, I could not open the trunk any more. However, when I was driving the message displays "tailgate open" and within a minute I heard the trunk closing (okay). Then when I park the car, I could open the trunk, close it the first time perfectly, but when I open and close the trunk the 2nd time, it will repeat the same issue as described above.
The auto repair shop technician suggested me to buy the "Rear SAM module" because he suspect it is bad. This rear SAM module cost $300 used one.
I really want to ask is the SAM the culprit? What went wrong with the SAM, can we clean it (how?) To make it good contact?
I really appreciate for your help, support
Best regards,
Tony

Hello KaseKenny1,

Thanks so much for your time looking into the issue in details.
Attached please see the clip video of how it has been happening. It happened exactly that I did explain, first time open the trunk no issue, close it no issue hearing the closing sound uh uh uh. Then open it second time ok, however, closing it hearing no sound, then could not open the trunk.
Then driving, see the message "tailgate open", keep driving few miles some time 5 min, some time, 8min randomly, then hearing the closing sound uh uh uh. Then when we stop, we could open the trunk the first time, then close, then open 2nd time no issue, but closing the second time having hearing no sound and can't open it. The issue repeatable like this.
I don't know how to fix it, I did using dirt cleaning, wd40 to clean a bit but no help.
I might have to end up buying the rear SAM Module and try it. Thanks so much for your advice.

I don't have a scan tool.
Tony

Hello KASEKENNY1,

Thanks a lot for your comments.
I will try to follow your instruction to close the trunk softly tomorrow and let you know the result.
In my earlier email, I have mentioned that I have seen this issue, phenomenon few months back until 2 weeks ago, when I opened the trunk and closed it, I heard the motor keep making noise uh. Uh. Uh. Then stop then uh. Uh. Uh then stop and continue doing that so I have to drive to the auto repair shop for technician to remove the panel and unplug the wiring.
Then I bought the new Tailgate Trunk Lift Door Hatch as shown in image attached and replaced it.
Therefore I'm not sure "the latch" that you mentioned is the Tailgate Trunk Lift Door Hatch that I bought or something else?
Appreciate that you could give me the part # or the image so I could buy to replace it
Thanks a lot for your advice.
Tony

Hi,

I have tried to close the trunk gently/softly but it did not help.
Thanks,
Tony

Replaced Rear SAM Module bought it on eBay for $299.00, it works perfectly. Could not believe that how the defect rear SAM module behaving like explained earlier.
Thanks so much Kasekenny1 you are awesome. This should be a good case study to share to everyone.
Tony

I have a different but connected issue on my W164 ML420 so I thought it might be worth adding it to this thread, if that is acceptable. My solenoid on top of the hydraulic pump is water damaged. The pump still runs. Does anyone know the correct resistance for the coil on the solenoid? I've cut back the rotten pins to get contact and get circa 2 ohms, which to me is too low.

Thank you.