sleepy hollow

My wife's CLK320 (60K miles) has a problem with the trunk actuator. Instead of a nice click and open when pressing the remote button on the driver's door or when using the key fob, there is a hideous buzzing noise for a second or two and the trunk stays closed.

It can be opened by pressing down firmly on the trunk lid while using any of the 3 techniques: driver door button, fob, or trunk lid handle. So, the mechanism is doing the same thing from all three actuation sources. The mechanical cylinder works fine.

I have spent some time examining the actuator setup and playing with the mechanical key/lock cylinder in order to isolate the two separate "systems". So far I am not sure exactly which part is failing. The parts diagrams at the OEM web sites are not good enough for me to figure out what to replace. Given the potential cost of a new control unit ($310), assuming that is the culprit, I'd want a high degree of confidence it is the failing part.

Can anyone help me further diagnose the problem? Diagrams or troublshooting/repair procedures would be a great help. I believe I have learned it is a pneumatic device?

If so, then perhaps there is a leak that makes the mechanism so feeble now.

Thanks.

Rudeney

I can almost guarantee that it's the lock mechanism. It has small plastic gears inside that just wear out. I had the same problem on the C240. The latch is around $100:

http://www.parts.com/parts/2005/MERC...component=Lock

It's fairly easy to replace. Just remove the trunk lid carpeting and a few bolts. Make sure you properly re-attach the manual opening cable. Also, you may have to change out the vehicle's wiring harness connector due to a redesign. This was the case on my MY2002 C240. The new lock part should include the new connector. You have to remove the pins from your connector and insert them into the new one. Of course there are no instruction for this, so I had to do it trial and error to see which wire went to which pin. Anyhow, if that's the case on yours, just ask and I'll go check one of the cars to see what color goes where for you.

sleepy hollow

Thanks, Rodney. I think that pretty much nails it. The sound I am hearing is entirely consistent with stripped plastic gears. I had no idea that it was gear driven. No wonder I was scratching my head when trying to observe/troubleshoot the mechanism. I was expecting more of a relay actuation, like in domestic cars, and looking for more "action" in the external cables, if that makes any sense.

I will let you know if I run into installation issues. Thanks for the offer. Great to be able to benefit from others' experiences.

I will order the part straight away. The site you sent me to seems to always have about the best prices as well. In case you have not found this one, it also has decent prices for some items (not the trunk lock in this case).

www.fcpeuro.com

Rudeney

One thing to know about parts.com - that company itself does not sell and ship the parts - they are just a middleman. They connect with car dealers all over the country to offer their low negotiated prices. Parts.com takes a fee and collects shipping fees (it's all disclosed on the order form), and then the dealer ships. Sometimes if you order multiple parts, they can come from different dealerships, but shipping is still the same. I've actually had them pay for FedEx next day service on a $2 bolt from one dealer, and the other $100 of my order from another. I guess this is just part of the dealer agreement with parts.com. Oh, and if there's a problem (i.e. wrong part), as long as you ordered the correct part and provided the VIN, the dealers take care of it. I ordered a new lower cover panel for my CLK (the one under the transmission) and some other things for the C240. I was very specific in the notes that the cover was for the CLK with its VIN, but they sent the one for the C240. The dealer (Naperville, IL) was very good to take care of it - sent me a replacement overnight and a label to return the wrong one.

sleepy hollow

Just wanted to close this one out. The new trunk lock arrived in about 3 days and I installed it in about 5 minutes.

Worked great except for one thing. For some reason now my remotes do not activate the trunk lock. Handle and switch on driver's door work fine. Batteries two months old.

Is there some reset procedure anyone can enlighten me about? I had to do this once with the windows.

BTW, I took apart the old mechanism and the gears are clearly slipping and not meshing properly when I move them manually, but none of them looks "stripped." Strange, as they look fine and look like they should be working. But I don't have any desire to disassemble the new one for comparison, so the mystery will remain.

Thanks, Rudeney.