Adding OEM VW keyless entry and alarm to your MK3 car

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Difficulty 2/5


On the a3/b4 passat and jetta, you can retrofit an alarm module from a jetta with keyless entry to gain keyless entry.

Why OEM?  Because it's designed to work with your car straight from the factory.  You only have to jump (meaning to splice one wire into another so that they are connected) a wire to get it to work properly.  

There are generic aftermarket modules available that work just as well and may be cheaper.  To use a generic aftermarket module, splice into the wires at the spare tire well for the lock vacuum pump and it'll work the same as this.  See a wiring diagram for more information.

First, test if you need the module.  Turn the car ignition to ON (not start).  
Close the doors, hood, trunk, etc.
With 1 key in the ignition to ON, turn and hold another key in the driver's door lock to UNLOCK and hold for 15 seconds, or until you hear a beep.  If you do not hear a beep, you need a module. 
To double check, you can remove the headlight switch.  If you see a silver metal box, you do not have keyless entry.  If you see a white box, you may have keyless entry. 

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Here is a picture of the white keyless entry box disassembled.

Here is a picture of the OEM silver alarm (NOT keyless entry, this is what you are replacing) box before being removed.

If you already have the keyless entry white box, refer to 1000 answered questions: keyless entry and alarm troubleshooting to determine why it isn't working.  You may also want to remove the module to check the part number.

Also note that if you have a wagon, there is no remote trunk release.  If you have a sedan, additional steps must be taken to add the remote trunk release function to the remote, found here: 1000 answered questions: adding keyless trunk release

Tools/Parts (click for new retail prices)

Keyless alarm module: (comes with 2 remotes if new) VW part# 1hm 937 045m , # 1hm 937 045q,  # 1hm 937 043b - white rectangular box w/2 plugs: (1 6 pin plug, 1 10 pin plug) FCC id# m3ghu01r
Keyless remote: (only for module # 1hm 937 043b) FCC id# m3ghu01wt (says clarion on the back) VW part# 1em 937 047a

Note: The FCC id numbers must match, except for the last letter.  T stands for transmitter (remote), R stands for receiver (module).  You must have a matching set for keyless entry to work.  Only some of the above part numbers are available new, if you are buying used, check the module's fcc numbers before ordering the remote.

Required tools:
wire, solder, soldering iron/gun or splice crimp connectors
phillips screwdriver

important circuit diagrams:
Alarm / Keyless entry circuit diagram from a jetta/golf 
Power door circuit diagram from a jetta/golf

Related links:
Troubleshooting faulty alarm/keyless entry
Adding keyless trunk release function


  1. Disconnect battery.
  2. Remove 2 phillips screws on the driver's side dashboard pad, tape screws to the pad so that they are not lost. (dia 1)
  3. Remove 3 phillips screws holding plastic fuse box cover and set aside.  Tape the screws to the plastic so that they stay with the plastic cover.
  4. Remove plastic cover over allen bolt and remove allen bolt with 3/16 bit. (dia 2)
  5. Check to see if the pad moves freely.  The allen bolt is the only thing that should be holding the driver's and passenger's side pads together.  Pull pad hard to separate the halves.  I suggest wearing gloves because there are sharp unfinished metal edges. (dia 3)
  6. Use a feeler gauge to loosen and pop out the headlight switch, disconnect switch and put aside.  
  7. There are 2 phillips screws holding the module in place. (marked by green dots in dia 4)  The bottom screw can be easily removed, the top screw can be easily removed if you gently bend the mounting plate to get to the screw. (dia 4)
  8. Unplug the 2 plugs.  Do not pull on the wires, pull on the plug, that's what it's there for.
    If you do not want to test it at this point, skip the next two paragraphs and go straight to "connecting jumper wire"

Diagram 1

Diagram 2

Diagram 3

Diagram 4

Before you install the alarm module, soldering a small insulated wire to the end of the antenna and then drilling a small hole in the plastic case to let the wire out will increase the range of the antenna.  The antenna is the coiled, covered wire in the below picture.  

The mounting screw is in a different location on the new box so I used some foam padding and a wire to move the mounting screw from the blue tape to the wire loop.  The wire is also shaped like a spring to hold the box tight.   



Initial testing of the module

  1. Plug in the new module and reconnect the battery, and prepare to run the following test.
  2. Program the remote by inserting 1 key in the ignition switch to ON (not start)  
  3. Close the doors, hood, trunk, etc.
  4. With 1 key in the ingition to ON, turn and hold another key in the driver's door lock to UNLOCK and hold for 15 seconds, or until you hear a beep, let go of the door key and let the key return to neutral.
  5. Press UNLOCK on each remote, you should now hear a beep.
  6. Turn the door key to UNLOCK, you should now hear another beep, remove all keys.
  7. The remote should now unlock the doors.  If it does not unlock the doors, begin troubleshooting, found here: keyless entry and alarm troubleshooting.
  8. The remote should NOT lock the doors.  The remote when locking, should only turn the red led on the door, the door should NOT lock.  The only exception is pre-1996 cars which did not have selective locking.  1996-1997 passats have selective locking and require a jumper to lock the doors.
  9. If you are not happy with the range of the remote, you can increase the range by adding a long wire that acts like an antenna, as seen above.  Loop it under the dash and secure in place. 

Connecting jumper wire

  1. If the remote successfully unlocks the door, but does not lock the doors (only turns on the red led), you must now add a jumper wire (a bridge/one wire spliced into another).
  2. Disconnect the battery - always disconnect the battery when doing electrical work.
  3. Unplug the keyless module.
  4. Splice a jumper wire from pin #7 on the "10 pin plug" (it should have a yellow wire with a red stripe, NOT a red wire with a yellow stripe but some cars had different colors on the wire) to the gray wire coming out of the door plug, pin #3.  There are 2 gray wires, choose the one that is closest to the front of the car, the one that is closest to the door hinge, this should be pin #3.  If you lock the driver's door with a key (battery connected), this wire should show 12V.  Make sure you use a long enough jumper wire!  Remember that it has to go back behind the dashboard. (dia 5)
    I suggest using a squeeze splice connector or crimp connector/tap.  You put both wires in a crimp and it cuts the wire insulation just enough to connect.  If you don't know what this is then just go to Radio shack and tell them you want a crimp connector for jumping/splicing two wires.  This is easier/more reliable/much faster than soldering.
  5. Shown in diagram 6 (alarm circuit diagram from a jetta) you want to connect the 2 green dots.  In the b4 passat, they are not connected, so you must add a jumper wire, represented by the yellow dot.  This will enable the remote to lock your doors as well.

Diagram 5

Diagram 6

Finishing steps

  1. After the wires are soldered and insulated, plug the module back in, connect battery, try testing the locking and unlocking, both should now work.
  2. The new module has a different mounting point from the old module, so use some method to secure it back - pipe straps or wires will work.  (dia 7)  I bent thick wire into a spring, padded it with foam tape ,and used the spring to hold the module in place.  The bottom loop is for the original phillips screw.  The blue wire is an antenna extension wire.
  3. The rest of installation is the reverse of removal.  

Diagram 7


If you need more DIY help on installing keyless entry module into your Passat or Jetta, please ask in the Volkswagen TDI discussion forum here: forums