In this article, we will go over what is involved with replacing the door lock actuators on the W210 Mercedes. These cars use a vacuum operated system to lock and unlock the doors. The system uses a vacuum pump mounted under the passenger seat to either suck or blow air through lines to each door. At each door, there is a vacuum diaphragm that over time can leak and eventually fail. By today’s standards, this type of system may seem a bit illogical. In fact, nearly everyone I told about the system said, “Why wouldn’t they just use a electric solenoid?” Back in the day, many mechanical systems on cars used vacuum to operate various components, such as flip-up headlights or windshield washers.
Nowadays, electronics are nearly foolproof and are cheap enough to use in almost any application. Mercedes started using vacuum operated locks sometime in the 1970’s, when modern electronics were still expensive and not quite reliable enough to be used in a system that would be used so frequently. The W210 Mercedes was one of the last cars produced that still used the older, proven vacuum system before finally converting to electrically operated door locks.
Unfortunately, as the cars age, the components of the vacuum system can deteriorate, eventually leading to leaks that will typically prevent one door from locking while the others lock with no problem. The one door can still be locked manually by pressing the lock button down; however on some cars like ours, there is no lock cylinder on the driver’s side door. This presents the problem of having to press the lock button down on the driver’s door with the door closed. Obviously, not many people are going to want to press the lock button down from the passenger side or climb over the center console to exit the car.
The first step in replacing the actuator is to disconnect the battery. Remove the small plastic plate at the bottom of the rear passenger seat. Underneath is a 11mm nut holding the negative terminal from the battery to ground. Remove the nut and pull the cable off.
Remove the screw holding the door latch cover in place. Once removed, take the cover off. Pry out the surround piece around the door handle. It just pops out. Underneath is a large Phillips head screw. Remove the screw and set it aside in a safe place.
Pry out the “SRS Airbag” cover piece. Below is a Phillips head screw. Remove the screw and set it aside in a safe place. Also unscrew the door lock button. Remove the trim plug underneath the door pull. Beneath is a Phillips head screw as well. Remove the screw. Now pry out the light switch along the bottom edge of the door panel. Disconnect the wires going to the light.
You’ll now need to take a large flat head screwdriver and pry the door panel off along the front bottom and back edges. There are a series of plastic clips holding it in. If you work your way around the edges, you’ll be able to remove the panel without breaking any of the clips. If some do get broken, it’s not a big deal as they are not expensive to replace (MBZ part number 011 988 76 78). There are nine of them around the perimeter of the front door panel. Once you have popped the edges of the door panel free, lift the door panel up to release it from the top edge of the door near the window. Once removed, look inside. You’ll see the metal hook connecting the door handle to the release latch. Lift the hook out to release it from the latch.
Now look at the backside of the seat adjustment switch. You’ll see the electrical harness going to the switch Pull the harness out of the switch. Also pull the harness going to the lower door light out of the door panel. With the door panel removed, you’ll see the plastic moisture barrier on the door panel. You’ll want to carefully peel this off the inside of the door starting at the rear edge of the door. The idea is to peel it off in just a way so that it can be glued back onto the door later. Just let the plastic drape over the speaker at the front of the door.
At this point you should be able to see the yellow vacuum line leading to the lock actuator. Reconnect the battery for a short mechanical test. We want to use the key fob or the key to actuate the vacuum pump. As you do this, put your ear up close to the actuator. Listen for any hissing. More then likely, you’ll hear it. If you do, this means that there is a leak in the actuator and it must be replaced.
The first step in replacing the door lock actuator is to disconnect the battery. Remove the small plastic plate at the bottom of the rear passenger seat. Underneath is a 11mm nut holding the negative terminal from the battery to ground. Remove the nut and pull the cable off.
You’ll now need to take a large flat head screwdriver and pry the door panel off along the front bottom and back edges (green arrows). There are a series of plastic clips holding it in. If you work your way around the edges, you’ll be able to remove the panel without breaking any of the clips. If some do get broken, it’s not a big deal as they are not expensive to replace (MBZ part number 011 988 76 78). There are nine of them around the perimeter of the front door panel.
Once you have popped the edges of the door panel free, lift the door panel up to release it from the top edge of the door near the window. Once removed, look inside. You’ll see the metal hook connecting the door handle to the release latch. Lift the hook out (green arrow).
Now look at the backside of the seat adjustment switch. You’ll see the electrical harness going to the switch (green arrow). Pull the harness out of the switch. Also pull the harness going to the lower door light out of the door panel.
With the door panel removed, you’ll see the plastic moisture barrier on the door panel. You’ll want to carefully peel this off the inside of the door starting at the rear edge of the door (green arrow). The idea is to peel it off in just a way so that it can be glued back onto the door later. Just let the plastic drape over the speaker at the front of the door.
Now pry out the plastic tab holding the
IRE sensor wiring harness to the door (green arrow). Also cut the zip-tie holding the harness to the mounting tab on the left of the door airbag (purple arrow). Pull off the vacuum connection going to the door lock actuator (yellow arrow). Use caution when pulling the vacuum line off. It can be fragile and break.
Unfortunately, the wiring harness for the
IRE sensor runs directly under the door airbag. You’ll have to drill out the rivets holding the airbag to the door frame in order to free the harness. Shown here is the bottom rivet. Make sure that you disconnect the two terminals from the battery and short them together. Wait at least 30 minutes for the whole system to discharge before removing the airbag.
Shown here is the remaining wiring harness clip behind the airbag (green arrow). Pop it out of the door to release the wire from the door. Keep in mind that you don’t want to re-attach the battery with the IR wiring disconnected as it could trigger the vehicle immobilizer. If the car’s security system detects that there is no signal from that door, it can think that the car has been broken into.
Pull the gasket out of the channel on the rear of the door. You want to find the small access hole inside the channel. This will allow you to access the small 4mm Allen bolt that retains the IR sensor/Door handle (green arrow). Carefully loosen the bolt until you can remove the IR sensor on the door handle. Don’t worry about dropping the bolt inside the door. It’s held captive inside the handle assembly inside the door.
Comments: when shorting out the cables before removing air bag do I let the cables stay together for 30 minutes?
January 21, 2015
Followup from the Pelican Staff: It's not necessary to short the cables together. Just disconnect the battery and allow the vehicle to sit for 15 - 20 minutes. - Nick at Pelican Parts
Comments: Very informative article on c220 door lock, but where is the rest of it? It looks like I have to remove one of the window guides in order to remove the lock actuator assembly.is this true? I don't mind doing it,just that I think it should have been mentioned. thank you.
January 18, 2015
Followup from the Pelican Staff: You may be correct, I recall the regulator having to come out. I will have someone check with the article author. - Nick at Pelican Parts
Comments: How do you change a fuel door actuator on a 1996 Mercedes S320? I could not open the door to fuel the car so I pulled on the actuator manual handle in the trunk and was able to open the fuel door. I have since ordered from Pelican a new actuator but do not know how to take the old one out to replace it with the one I got from your company. Can you help? Thanks
December 31, 2014
Followup from the Pelican Staff: We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.
I would think it is mounted in the fender, behind a trim panel. Check the trunk area. - Nick at Pelican Parts
Comments: Linkages? Do you mean take it apart and inspect the cable?
I am new to this stuff. Akso thanks for your help on this.
December 9, 2014
Followup from the Pelican Staff: Yes, the cables and the levers / links they attach to. - Nick at Pelican Parts
Comments: No it works fine opens and close on the door handle
December 9, 2014
Followup from the Pelican Staff: Sounds like the latch might be your problem. I would inspect it and the attaching linkages. - Nick at Pelican Parts
Comments: I have a clk320 1999. My drivers door out side handle works bout 10% of the time and when it does the door does not open all the way it hangs. Do i need a need lock act.?
December 7, 2014
Followup from the Pelican Staff: Does the handle remain extended? (in the pulled position) If so, the handle or brakcet may be fault.y - Nick at Pelican Parts
Comments: I have a 2000 ML550 and none of the locks are engaging with the remote. They also won't lock if I use the key. What do you think the problem is? If I press the lock or unlock button on the key it does not do anything
November 24, 2014
Followup from the Pelican Staff: Sounds like the module thinks a door is open. Check if one of the doors reads open when all are closed. You will need a Mercedes-Benz scan tool. - Nick at Pelican Parts
Comments: I have a 1997 E 320 with a problematic door check strap. IT was not working smoothly at all so I pulled the door panel off and saw a screw was completely out. I fastened back but the door check still makes alot of noise and it doesnt work smoothly. I tried some Lithium grease but still no fix. How do you access the door check to pull it out? Do I have to drill out rivets in order to get it out?
September 30, 2014
Followup from the Pelican Staff: The check is probably rusty. I think there is one bolt in the door jamb and two on the door side. I do not think you have to drill any rivets. - Nick at Pelican Parts
Comments: I have a 2008 ML350 that the rear hatch actuator try's but just wont let the door open. Anyone replaced one of these, or have any suggestions. How long have hatchbacks been around? Automatic trunk lid openers even longer, how complicated does it have to be? Oh and don't forget to take away the ability to open it manually with a $400.00 Key!
September 24, 2014
Followup from the Pelican Staff: I would check if the pump is corroded or if the fluid level is low. - Nick at Pelican Parts
Comments: Thanks again Nick-will get on with it and let you know how turns out-BTW car is exact replica of your 84 SL picture.
August 10, 2014
Followup from the Pelican Staff: Thanks. Let me know what you find. - Nick at Pelican Parts
Comments: Thanks Nick,your reply is appreciated.The problem is a Chinese puzzle
If drivers inside lock in unlocked position- in neither drivers or passenger door will key turn to lock car
If drivers inside lock in locked position - then drivers door can be unlockedalong with trunkbut still will not lock but now passenger door can be unlocked and locked.
very confusing-? a door latch malfunction or vacuum problem?
August 8, 2014
Followup from the Pelican Staff: From that description, I would say door latch. - Nick at Pelican Parts
Comments: 1984 380 SL key will not turn to lock door on drivers side while passenger side key will still turn but also not lock vehicle.Still able to lock from inside door and also lock trunk.Does this sound like a vacuum leak or an inherent failure of lock mechanism.No idea from dealership.
August 5, 2014
Followup from the Pelican Staff: Is just the driver door not locking? If so, likely the driver latch. - Nick at Pelican Parts
Comments: How do I put the airbag bag on/in so that it will function properly since we drilled the rivets to remove?
July 23, 2014
Followup from the Pelican Staff: It would have to be reinstalled the way it was originally attached. You will likely need to use the correct rivets to attach it. Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
Comments: My body shop guy tells me I need to replace the Driver Door Lock Actuator for 1970 Mercedes 280SE - 108 series. Any idea where to find this part
June 6, 2014
Followup from the Pelican Staff: It's in the door, attached to the latch. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
doors want lock
Comments: I have a S320 benz my doors will not lock . I have to use my ley What will
lock. I have to use the key What will
Make it do that?
May 7, 2014
Followup from the Pelican Staff: Could be a faulty actuator or control module. I would start by checking the vehicle for fault codes. - Nick at Pelican Parts
Comments: I have a 2001 S600. The front passenger door does not suck close. All others do. I am looking for the lock unit.
February 4, 2014
Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
Comments: Do you have a guide for a 2008 c350 w204? I'm having trouble removing the actuator. Thank you!
January 13, 2014
Followup from the Pelican Staff: We currently do not. If we have the chance to perform the repair, we will be sure to document it. - Nick at Pelican Parts
Comments: hello, my 1997 E 420 rear passenger side door lock will lock if car is triggered by the lock function or via remote yet will not unlock via the same two systems. Is this typical? are there two different vacuum lines?
November 7, 2013
Followup from the Pelican Staff: No usually the PSE pump supplies vaccum to open locks and pressure to close. Sounds like you have a vad PSE unit - Kerry at Pelican Parts
Comments: How do you get a new ir sensor for the driver door , mine has been puncture . Ir sensor in the rear view mirror does not lock or unlock the doors. But when ignition switche is in on position the counsel lock does work , locks and unlocks . What part do I need .
Allready took it to mercedes dealer , could not locate the problem .
October 25, 2013
Followup from the Pelican Staff: It is too difficult for me to tell if you need an ir module or the PSE module without having a scan tool connected to the car while you were hitting the remote button. Tell you mechanic to scope the wire from the remote control module to the PSE module to see if it is getting a signal. That's the way it is with American cars. Out ir sensors are in the rear view mirror on older cars and in the door handle on newer ones - Kerry at Pelican Parts
Comments: The 2002 E series doesn't need the airbag drilled out or disconnected, the IR wire is routed around the top of the airbag and the connector is accessible on the rearward side of the airbag. Also, the door handle is held on the rear side by a spring attached to the door handle receiver inside the door. It must be put back behind the latch actuator lever and this spring when reassembled. You have to reach in on the inside to compress the spring while reinserting the outer door handle.
August 26, 2013
Followup from the Pelican Staff: Thanks for the tips for our readers - Kerry at Pelican Parts
Comments: Hello. Any tech article on the rear door lock actuator on the w210?
July 13, 2013
Followup from the Pelican Staff: Sorry, the W210 rear door procedure has not been done yet.
This should be on the future DIY list.
Charles n Charge
Comments: The heat melts the glue onto the locking rod. you can take some kneedle nose vice grips and pull really hard.but you will probally damage your plastic lock pull
December 28, 2012
Followup from the Pelican Staff: This may work for getting it open.
However, the latch mechanism should be removed, cleaned, lubricated and exercised before reinstalling.
If it still does not work, it must be replaced.
Comments: Most of the time it is the actuator in the rear door that fails. Do you have a tutorial on that?
September 25, 2012
Followup from the Pelican Staff: I presently have the dashboard out of the W201. When I complete those projects, I will bring the W210 into the shop and create a tech article on the W210 rear door actuator.
- Steve at Pelican Parts
Check out some other sample projects
from the book: