soot1
Veteran Member
- Joined
- Nov 6, 2009
- Location
- Houston, TX
- TDI
- Currently none. Formerly: 2010 VW Jetta TDI 6M, 1993 Dodge Ram W250 Cummins 5M 4WD, 1990 VW Jetta Diesel 5M, 1986 VW Jetta Diesel 5M, 1980 VW Uabbit Diesel 4M. Currently driving 2018 Toyota 4Runner SR5 4WD.
Over the past two years or so, I've been experiencing issues with the driver's door latch. In the beginning, my specific symptoms were that every now and then, when locking the door with the electronic key fob, the door would not lock or unlock. It was always only the driver's door, all others work just fine. The red LED in the driver's door would stay on permanently instead of flashing when attempting to lock the door. When I pulled the door handle, the door would open and the alarm was activated. Alternately, when unlocking the door, the LED would go out, indicating the door is open, but it was still locked. As time went by, this became more and more frequent, so I made it a habit always to check whether the door is locked before leaving the vehicle. The next symptom that also appeared insidiously was that the alarm at one point no longer sounded when the door was open with the LED on. Sometimes, when I didn't succeed to lock the door on a first try, I would unlock it and lock it again. The second attempt was usually successful. However, as time went by, even this trick stopped working , and about 3 months ago, the key fob stopped working altogether. At that point, the only way to lock or unlock the driver's door was to insert the key into the lock and turn it.
I did some research on this issue, and there are some reports of defective microswitches in the electrical part of the latch. This sounded plausible, as the microswitches tell the on-board computer whether the door is open or closed, and locked or unlocked. After viewing a couple of videos on Youtube on how to remove the lock cylinder, the door skin and how to take the latch apart, I decided to give it a try. Originally, I had a new latch assembly (VW part number 3B1837015AT) on my list of parts I planned to buy with my $500 goodwill dealer card, but I figured if I can fix the old one, I'll save myself at least $140, which is what I would pay for it at keffervw.com (lowest on-line price I could find). So this morning, I went to the garage and began removing the latch. First, I removed the plastic shield from the door edge. You just peel it off, no tools required, it holds to the door with several snap-on buttons. Next came the removal of the door lock cylinder, and it was also a breeze, I encountered no problems (you will need Torx 20 screwdriver). Next was removal of the door handle cable from the handle. Before I pulled the cable end from the groove, I marked its position with a silver pen (excellent contrast on the black plastic). This step will save you some headaches when putting everything back together. Next was removal of the door handle and a Torx 20 screw that holds the door skin to the lock cylinder subframe. My next move was to duct-tape all edges of the door and front fender to protect them from accidental dings or scratches. Removal of the door skin was next, and it is also a pretty straightforward operation. Just take note of which type of screw goes to any particular location, as there are three different types. All screws are Torx 30. After removing the door skin, the latch comes into view. The removal is also fairly easy. Start with the two triple-square screws (6 mm) that hold the assembly to the door. Once you remove them, push the latch assembly with the shield upwards and then towards the front of the vehicle (the whole assembly hangs on a tab, similar to a picture on a wall). Next, remove the cable that opens the door from inside. The outer shell of the cable is secured to the latch assembly, and it takes considerable force to remove it. When you are done with that, unhook the end of the cable from the lever. Next, using small flat screwdriver, remove the electrical connector. You will notice that the rain shield is secured to the latch assembly with three snap fingers. Remove the rain shield, and you are left with the bare latch assembly.
I then went upstairs to take the latch apart. It is composed of two sections, mechanical and electrical. They are held together by one Torx 15 screw. I removed this screw and wiggled the two sections apart. Being certain the problem is somewhere in the electrical section, I proceeded to take it apart. The electrical section is made of two clamshells that are held together with several Torx 10 screws. Once I removed them, the subassembly came apart. Inside is a small printed circuit board that holds three microswitches and the electrical connector. Another remote microswitch is located in the mechanical section, and is connected to the circuit board with rather rigid wires. Since I suspected the microswitches to be the culprit, I proceeded to measure with an ohmmeter whether they function correctly. They checked OK, so I focused my attention on the servo motor, which is the only other electrical component in the shell. Using an ohmmeter, I measured DC resistance of the winding, and that's when I found something strange - 1200 ohms. The resistance should be a couple of ohms at the most. So, next I pulled a power supply, set it to 12 V, and connected to the motor. It turned about half a revolution, and stopped. Culprit identified. Curious what can possibly be wrong with a small DC motor, I proceeded to take it apart. It is typical small DC motor made by Mabuchi, part number FC-280PD-20150. The metal case of the motor that holds the magnets and rear bearing has two tabs that secure the front end of the motor, which is made of plastic and holds the front bearing and the two brushes. It took some effort to bend the two tabs out of the way. I then pulled the metal casing with the rear bearing off the shaft, and the damage was in plain sight: the commutator was completely blackened where the brushes came into contact with it. I suspect that during the assembly, bearing grease somehow ended up on the commutator, and the arcing that is normally present when the motor runs turned the grease into clump of carbon. I then carefully removed the brushes from the commutator and slid the entire plastic front part of the motor as far as I could to get better access to the commutator. Using a narrow strip of 600 grit sandpaper, I removed the carbon deposits from the commutator until only clean copper showed. I then removed the brushes from the front cover and cleaned them too. Next, I washed the inside of the front motor cover in solvent, as it was all covered in black dust and bearing grease. Once everything dried up, I reassembled the motor and hooked it up to 12V. As expected, it came back to life. Quick ohmmeter check showed 3 ohms, which is what I would expect. I then reassembled the electrical section, attached it to the mechanical section, then the rain cover, and went downstairs to the garage to put it all back together. About an hour later, when the latch was inside the door, the door skin, handle and lock back in place, the moment of truth came when I shut the driver's door and pushed the "LOCK" button on the key fob. It worked flawlessly !!!!!
Moral of the story - if your door latch isn't working properly and you pull it out and find out the microswitches are OK, check if the servo motor might be the root cause. Of course, now that the latch is working, I'll have to come up with something else to buy with the money I set aside for the new latch. Also, my apologies for not attaching any pictures. I tried to finish as soon as I could (it still took almost all day), plus my hands were greasy and grimy all the time, so touching a camera was out of the question.
I did some research on this issue, and there are some reports of defective microswitches in the electrical part of the latch. This sounded plausible, as the microswitches tell the on-board computer whether the door is open or closed, and locked or unlocked. After viewing a couple of videos on Youtube on how to remove the lock cylinder, the door skin and how to take the latch apart, I decided to give it a try. Originally, I had a new latch assembly (VW part number 3B1837015AT) on my list of parts I planned to buy with my $500 goodwill dealer card, but I figured if I can fix the old one, I'll save myself at least $140, which is what I would pay for it at keffervw.com (lowest on-line price I could find). So this morning, I went to the garage and began removing the latch. First, I removed the plastic shield from the door edge. You just peel it off, no tools required, it holds to the door with several snap-on buttons. Next came the removal of the door lock cylinder, and it was also a breeze, I encountered no problems (you will need Torx 20 screwdriver). Next was removal of the door handle cable from the handle. Before I pulled the cable end from the groove, I marked its position with a silver pen (excellent contrast on the black plastic). This step will save you some headaches when putting everything back together. Next was removal of the door handle and a Torx 20 screw that holds the door skin to the lock cylinder subframe. My next move was to duct-tape all edges of the door and front fender to protect them from accidental dings or scratches. Removal of the door skin was next, and it is also a pretty straightforward operation. Just take note of which type of screw goes to any particular location, as there are three different types. All screws are Torx 30. After removing the door skin, the latch comes into view. The removal is also fairly easy. Start with the two triple-square screws (6 mm) that hold the assembly to the door. Once you remove them, push the latch assembly with the shield upwards and then towards the front of the vehicle (the whole assembly hangs on a tab, similar to a picture on a wall). Next, remove the cable that opens the door from inside. The outer shell of the cable is secured to the latch assembly, and it takes considerable force to remove it. When you are done with that, unhook the end of the cable from the lever. Next, using small flat screwdriver, remove the electrical connector. You will notice that the rain shield is secured to the latch assembly with three snap fingers. Remove the rain shield, and you are left with the bare latch assembly.
I then went upstairs to take the latch apart. It is composed of two sections, mechanical and electrical. They are held together by one Torx 15 screw. I removed this screw and wiggled the two sections apart. Being certain the problem is somewhere in the electrical section, I proceeded to take it apart. The electrical section is made of two clamshells that are held together with several Torx 10 screws. Once I removed them, the subassembly came apart. Inside is a small printed circuit board that holds three microswitches and the electrical connector. Another remote microswitch is located in the mechanical section, and is connected to the circuit board with rather rigid wires. Since I suspected the microswitches to be the culprit, I proceeded to measure with an ohmmeter whether they function correctly. They checked OK, so I focused my attention on the servo motor, which is the only other electrical component in the shell. Using an ohmmeter, I measured DC resistance of the winding, and that's when I found something strange - 1200 ohms. The resistance should be a couple of ohms at the most. So, next I pulled a power supply, set it to 12 V, and connected to the motor. It turned about half a revolution, and stopped. Culprit identified. Curious what can possibly be wrong with a small DC motor, I proceeded to take it apart. It is typical small DC motor made by Mabuchi, part number FC-280PD-20150. The metal case of the motor that holds the magnets and rear bearing has two tabs that secure the front end of the motor, which is made of plastic and holds the front bearing and the two brushes. It took some effort to bend the two tabs out of the way. I then pulled the metal casing with the rear bearing off the shaft, and the damage was in plain sight: the commutator was completely blackened where the brushes came into contact with it. I suspect that during the assembly, bearing grease somehow ended up on the commutator, and the arcing that is normally present when the motor runs turned the grease into clump of carbon. I then carefully removed the brushes from the commutator and slid the entire plastic front part of the motor as far as I could to get better access to the commutator. Using a narrow strip of 600 grit sandpaper, I removed the carbon deposits from the commutator until only clean copper showed. I then removed the brushes from the front cover and cleaned them too. Next, I washed the inside of the front motor cover in solvent, as it was all covered in black dust and bearing grease. Once everything dried up, I reassembled the motor and hooked it up to 12V. As expected, it came back to life. Quick ohmmeter check showed 3 ohms, which is what I would expect. I then reassembled the electrical section, attached it to the mechanical section, then the rain cover, and went downstairs to the garage to put it all back together. About an hour later, when the latch was inside the door, the door skin, handle and lock back in place, the moment of truth came when I shut the driver's door and pushed the "LOCK" button on the key fob. It worked flawlessly !!!!!
Moral of the story - if your door latch isn't working properly and you pull it out and find out the microswitches are OK, check if the servo motor might be the root cause. Of course, now that the latch is working, I'll have to come up with something else to buy with the money I set aside for the new latch. Also, my apologies for not attaching any pictures. I tried to finish as soon as I could (it still took almost all day), plus my hands were greasy and grimy all the time, so touching a camera was out of the question.