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Door Control Unit Replacement
 
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Pelican Technical Article:

Door Control Unit Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$325

Talent:

**

Tools:

Trim removal tool, T30 Torx driver

Applicable Models:

Mercedes-Benz C250 (2012-14)
Mercedes-Benz C300 (2008-14)
Mercedes-Benz C350 (2008-14)

Parts Required:

Control unit

Hot Tip:

Pry as close to the clips as possible

Performance Gain:

Working door systems

Complementary Modification:

Clean the windows

There is a door control unit mounted to the inside door component carrier that controls the functions of the components on the door. It is also used for diagnosing trouble with the systems on the door. While you can access the control unit for releasing the wiring when replacing the outside rear view mirror as well as using it for diagnostics, you must remove the door panel to replace the unit.

If you are working with the trim pieces on your Mercedes you really should buy some flexible plastic tools of different shapes and sizes that are used in removing trim pieces. They work much better than a flathead screwdriver, and there is nothing worse than ruining a "do-it-yourself" project by scratching up your car or damaging expensive interior pieces. Pelican sells a full line of these tool sets for under $20.

The control unit is located on the forward part of the door behind an access panel (red arrow).
Figure 1

The control unit is located on the forward part of the door behind an access panel (red arrow).

To access the panel use a trim removal tool and pry the end of the panel forward and out.
Figure 2

To access the panel use a trim removal tool and pry the end of the panel forward and out.

You can use this opening to remove the wiring connections when replacing the outside mirror as well as running diagnostics (red arrow).
Figure 3

You can use this opening to remove the wiring connections when replacing the outside mirror as well as running diagnostics (red arrow). To replace the unit you will need to remove the door panel.

When removing the door panel begin by placing the window in the lowest position it will go (green arrow).
Figure 4

When removing the door panel begin by placing the window in the lowest position it will go (green arrow). There are two trim pieces you will need to move/remove before removing the panel. One is the window trim piece where it meets the door panel (red arrow), and the other is the triangular speaker cover by the A-pillar (yellow arrow).

There is a fastener under the window trim piece that you will need access to.
Figure 5

There is a fastener under the window trim piece that you will need access to. Use a trim removal tool and separate the trim piece from the weather stripping on the outside of the doorframe (red arrow).

With the trim piece out of the weather strip channel use your trim tool and separate the piece (red arrow) from the doorframe.
Figure 6

With the trim piece out of the weather strip channel use your trim tool and separate the piece (red arrow) from the doorframe. You can now access the fastener (yellow arrow). This fastener has varied over the years from a clip to a T30 Torx screw.

Next, remove the triangular cover by prying it out from the area around the mirror.
Figure 7

Next, remove the triangular cover by prying it out from the area around the mirror. If yours has been removed before you can probably do this with your hands. If not use your trim removal tool (red arrow).

With the section around the mirror loose push the piece forward (red arrow) and out from the door.
Figure 8

With the section around the mirror loose push the piece forward (red arrow) and out from the door. The piece can just hang by the small speaker wire or you can disconnect it.

Use a T30 Torx and remove the three T30 Torx bolts; one is under the trim piece you removed, while the two others are below the armrest (red arrows).
Figure 9

Use a T30 Torx and remove the three T30 Torx bolts; one is under the trim piece you removed, while the two others are below the armrest (red arrows).

There are nine clips (red arrow) that hold the door panel in place.
Figure 10

There are nine clips (red arrow) that hold the door panel in place. Some of these clips might break or stay in the door when you are removing the panel. You want to use the proper door panel trim removal tool and get as close to the clips as possible. Prying them out will take a surprising amount of force, and you want to avoid having the plastic section of the panel that holds the clips break. Also do not pull on the panel with your hands, as you risk bending or damaging the panel itself.

This photo shows the approximate location of the clips and where you want to insert the tool.
Figure 11

This photo shows the approximate location of the clips and where you want to insert the tool. Make sure the tool is seated around the clip before prying on it.

With all the clips free you want to lift the panel up and out from the channel on the top of the door (red arrow).
Figure 12

With all the clips free you want to lift the panel up and out from the channel on the top of the door (red arrow). The door lock pull will stay on the door so you will have to lift the panel over it.

Tilt the panel towards yourself and slide the door pull cable (red arrow) out from the support in the door panel (yellow arrow).
Figure 13

Tilt the panel towards yourself and slide the door pull cable (red arrow) out from the support in the door panel (yellow arrow). Unhook the Bowden cable from the handle (green arrow).

Remove all of the wiring connections plugged into the control unit (red arrows).
Figure 14

Remove all of the wiring connections plugged into the control unit (red arrows). These are color coded so you cannot mix them up when reinstalling.

Slide the upper wiring harness from the unit by releasing the small tab on the clip (red arrow) and sliding off the unit (yellow arrow).
Figure 15

Slide the upper wiring harness from the unit by releasing the small tab on the clip (red arrow) and sliding off the unit (yellow arrow).

You can remove the wiring connection for the airbags without separating it by releasing the tab on the connector (red arrow) and sliding it off the bottom of the unit.
Figure 16

You can remove the wiring connection for the airbags without separating it by releasing the tab on the connector (red arrow) and sliding it off the bottom of the unit. Next, squeeze together the clip on the front of the control unit. Lift it out, and slide the unit forward and off the mount (yellow arrow).

With the unit off you can slide it forward and off the mounting holes (yellow arrows) that the plastic nubs on the back of the unit sit within (red arrows).
Figure 17

With the unit off you can slide it forward and off the mounting holes (yellow arrows) that the plastic nubs on the back of the unit sit within (red arrows).

Check the door clips before reinstalling the door panel.
Figure 18

Check the door clips before reinstalling the door panel. This photo shows the location of the clips (yellow arrows). You can see how two of them (red arrows) stayed in the doorframe when we removed the panel.

If the clips have not broken you can just pry them out of the door and reinsert them into the panel.
Figure 19

If the clips have not broken you can just pry them out of the door and reinsert them into the panel. It is a good idea to order a few spare clips before you begin in case you damage a few so you will not be hung up upon reassembly waiting for clips. Installation is the reverse of removal.

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Page last updated: Fri 12/9/2016 02:56:19 AM