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.
Figure 1
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.
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 (green arrow). Below is a Phillips head screw. Remove the screw and set it aside in a safe place. Also unscrew the door lock button (purple arrow).
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.
As you pull the IR sensor out, it should detach itself from the wiring harness connector underneath. If not, use a small screwdriver to gently separate it.
Pull the door handle back towards the edge of the door (green arrow). This will detach the handle from the hinge point at the front. Once loose, set the door handle aside.
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.
roy@pelicanparts.com
Chistoso
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
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