Door Locks

[dksix]

I have a 1992 325i sedan . The problem is that sometimes when I lock my doors ( either inside by hand or outside with key) they unlock themselves after about 3 seconds . It has done this with the key in the switch and out of the switch , while the car is running and shut off . I can see no pattern as to when it will unlock itself and not .

[Wayne 962]

See here:

One of the most common problems with older cars is the existence of intermittent and annoying electrical problems. Example: a dashboard light goes on when you hit the brake, but only when the rear defogger is on, or the radio only works when you are in reverse. As bizarre as it sounds, electrical problems like these have become more common as cars have become increasingly complex. Unfortunately, they can be quite difficult to fix.

What typically goes wrong with the wiring on these cars? Several things can happen. First and foremost, every time the car is sold, there is a big chance the new owner will do some modification to the wiring that only he or she will know about. The installation of a new stereo, Euro-headlamps, a radar detector, or the worst of all, an aftermarket alarm system, can seriously mess up your wiring configuration if not performed correctly. You’re left holding the mess, armed with only a few sporadic clues as to what is causing the problem. Troubleshooting electrical problems is a tough chore, and one that most automotive repair shops will not perform without telling you they will charge you their $80-an-hour diagnostic fee.

This project will give you some tips for troubleshooting your electrical system, but it’s not meant to be a step-by-step guide for fixing all of your problems. That would take almost as many pages as are contained in this book!

The first step in troubleshooting is to make sure that you are armed with all the information that you can get. Namely, the most important item you need to get your hands on is a copy of the electrical diagrams for your year car. At the time of this writing, they are available from a few sources. BMW has published books with extensive electrical diagrams in the past, but these can be difficult to find at times. Bentley Publishers prints manuals for most BMW 3-Series cars with summarized electrical diagrams in the back. These are certainly a good starting point for troubleshooting.

One of the most common problems is a continuous drain on the battery. One example would be a situation where you leave the car sitting for a week or two, and the battery becomes completely drained. This means that something is “on” inside the car, bleeding the battery of power. Start your troubleshooting process by disconnecting your battery ground, and connecting an ammeter to the battery negative and to the chassis. The ammeter will show the amount of current that your electrical system is draining from the battery. When you hook the meter up, it will most likely show that there is some small current flowing through the system. Don’t start the car or turn on any electrical accessories, because this might blow up your meter. Disconnect the front luggage compartment light before beginning any testing.

Now, move to the fuse box in the front engine compartment, and start removing fuses. Carefully watch the ammeter to see if the current drops to zero when a particular fuse is pulled. If it does, then you have successfully isolated the electrical circuit with the problem. You are more than halfway to solving your problem. Look at the electrical diagrams and you should be able to tell what components are located on that circuit. Try disconnecting each one, while watching the ammeter, and you should find the culprit. If pulling fuses doesn’t reveal anything, try pulling out the various relays. Sometimes a relay will be powered on, but the device it controls will be disconnected. This may lead to gradual battery drain.

Another common electrical problem is the device that just won’t work. If you carefully look at the electrical diagrams, you will notice that there are actually six points of failure for most electrical devices. For lack of a better example, we’ll use a horn to explain and demonstrate the electrical troubleshooting process.
Starting from the rear of the electrical chain, the first point to be concerned about is the actual device itself. You can start the troubleshooting process by testing the horn. Unplug it, and apply 12V DC to the horn to see if it will make a sound. It if doesn’t then you have a problem with your horn.

While the horn is unplugged, another excellent test to perform is to check the electricity in the wires leading to the window motor. If you press the horn button on the steering wheel, and there is no power going to the wires that power the horn, then the problem lies somewhere else.

The next spot to check would be the relay for the horn. Consult the electrical diagrams to determine which one is the correct relay. When the horn button is pressed, the relay should make a slight clicking noise on and off. Swapping out relays with one that is known to work is a good method of checking the proper operation of the relay as well.

If the relay checks out, then you want to make sure that the fuse is still good. Identify the proper fuse, and check to make sure that it has not blown. Also, the spade-type fuses that BMW uses are sometimes susceptible to corrosion building up on the terminals. Make sure that the fuses are clean and securely seated. If necessary, check the continuity across the two points that hold and mount the fuse.

Many electrical components on the car are also switched through the ignition switch—allowing them to be turned on and off with the ignition. If a device such as a window motor doesn’t work along with a host of other equipment, then you might have a faulty electrical ignition switch. One clear symptom of this is the dashboard lights and other equipment turning on and off as you jiggle the key back and forth. For ignition switch replacement procedures, see Project XX.

The switch for the device itself may be faulty. In the case of the horn, the switch is mounted in the center of the steering wheel. Remove the wheel and check the switch with a continuity tester to make sure that it is working properly.

Finally, if all the other tests fail to locate the problem, the wiring may be at fault. Especially on older cars, the wires have a tendency to become brittle, and sometimes break, even if the outer insulation is intact. Using a continuity tester, check each of the wires in the harness that powers the blower motor to see if any have lost continuity.

If all of these steps fail to pinpoint the problem, then you probably made a mistake somewhere along the line, or there might be a short circuit somewhere in the switch or the wiring of the car. Only painstaking testing using a continuity tester will be able to locate such a problem.


Picture 1: The fuse box is at the heart of your BMW’s electrical system. Located on the rear-left side of the engine compartment, the relays and fuses inside are sometimes vulnerable to corrosion and failure. Typically when I encounter an odd electrical problem, I check the fuses and the relays first – they are the easiest and cheapest solution to annoying electrical gremlins.

Picture 2: In particular, some cars may have known wiring issues which show up as strange electrical problems on many cars. One prime example of this is the faulty trunk wiring on the E36 3-Series. If your BMW’s alarm system repeatedly refuses to arm the car, instead giving me the signal that a door was open or ajar, there may be a problem with your trunk wiring. Open the truck and peel back the black insulation that connects the car to the trunk lid. As shown in the photo on the left, repeated open and closing of the trunk has made the wires and insulation brittle and has caused it to crack. Solder the two broken wires together and cover any missing insulation with tape as shown in the right photo.

[n.10.z]

I doubt this will help but in my '93 325is the driver interior door handle doesn't always completely return to the closed position and will cause the locks to do the same thing...

[Tim Polzin]

Here is a referenced fault:

Doors: If the central locking system unlocks itself after being locked or locks itself after being unlocked, the actuators could be defective or the trunk lock may need to be adjusted. (1992-93)

http://auto.consumerguide.com/auto/used/reviews/full/index.cfm/id/2116

Tim