Friday, November 25, 2016

Repairing Audi A4 B8 8K door not unlocking with remote fob

When you buy a pretty premium saloon, you would expect reliability. However, I have found that the german engineering of the Audi a bit underwhelming in terms of both reliability and ease of repair. Too often, small little niggley things have given up the ghost on the A4. The latest to go was locking mechanism on the drivers side door. When I tried to unlock the door with the remote key fob, the door made made a grumble but failed to unlock. It would require a second press of the fob to unlock the door, or else it wouldnt open at all. Instead, I would have to roll down the windows with the fob and open the door by reaching in and opening it from the inside.
I also noticed that the automatic locking of the door when the vehicle went over 30kph was making a strange noise on the drivers side.

I tried a few different solutions outlined on the various forums:

  • Pull the outside and inside handle at the same time until you feel it click: This appeared to work for a while, but failed again. 
  • Spray WD40 over all the moving parts including lock tumbler and handle cable: No effect
  • Dismantle door lock module and grease all parts: no effect
Using the VAG-COM VCDS diagnosis software and cable, I found a that the door lock module was throwing a "outside limit" error. Worse again, after a while, the issue appeared in the passengers side door too. Due to the noise that the locking mechanism made, I suspected the door motor. As such, I removed the trim and then the paneling of the door. There are about 6 torx screws that you have to remove to unfasten the paneling. Then you have to start pulling out the panel from the bottom. once you get the top, you can lift it upwards to remove it. Next, you can remove the blue internal door handle cable by unhooking it from the door handle side. Once that is done, you have to remove the outside door handle cable from the lock module. Reach into the door frame and twist the yellow catch on the end of the cable going into the door lock module. Next, remove a rubber gromit on the edge of the door frame to expose a grub screw securing the lock tumbler. Loosen this, and pull out the lock tumbler from the outside. Then to remove the door lock module, you will have to remove two large bolts from the outside edge of the door frame. Then you can reach in and remove the loosened door lock module.

Take the module to your work bench and remove all the screws on the outside. Open up the small gray hatch window. You will see two axels coming out from the main housing into the locking mechanism. Insert a flat screwdriver and prise the axels from the lock mechanism. You will be left with just the main housing. Using a spludger tool, prise the two half of the housing apart. Inspect the two halves when apart- if the water proof gromit has come loose, press it back into place.

Inside, you will see the two motors of the module. Remove the largest. Clean the two contact that insert into the motor. I used some fine (2000 grit) sandpaper. At this stage, I tested the motor using a 12v supply and found that it struggled to turn without help. There was obviously something wrong with it. Using a small screwdriver, lift the two tabs on the end of the motor. You can then prise the end off the motor. There was much carbon dust in the motor from the brushes. As such, I tapped the motor on the desk to knock it out. The commutator on the motor was blackened from the brushes. Again, with the fine grit sandpaper, this was quickly cleaned up. You can remove the brushes with a sim card removal tool. I cleaned these up with a small rag. I put the motor back together and tested it with a 12v supply. It ran perfectly.

Finally, you can put everything back again. Using the VAG-COM VCDS diagnosis software and cable, I reset the error codes. I tested the door, and it worked perfectly!. A month later and it still hasnt given any problems or caused errors in VCDS.

1 comment:

  1. I’m impressed, I must say. Seldom do I come across a blog that’s both educative and interesting, and without a doubt, you have hit the nail on the head. The problem is an issue that not enough folks are speaking intelligently about. Now i'm very happy I stumbled across this during my hunt for something regarding this.
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