How to Diagnose and Fix Your Power Windows

Don’t over complicate the diagnosis and get out of your own way. Get out of your own way and don’t over complicate the diagnosis! No matter how you say it, this is great advice that I wish I’d followed. If you’re having power window trouble, don’t do what I did.

Here’s a little ditty about when I did not follow my own advice. At the end of 2013 I purchased the car for my eldest son after he graduated from college. The car was a used 2002 BMW 325i. This was a 10-year-old car that was in great shape. I thoroughly went through the engine and chassis and made repairs to all the systems. I replaced all of the parts that are known to fail on a vehicle of its age. Everything worked on the inside of the vehicle except the two rear door power windows. They were dead. Completely dead. Both front windows worked fine but the passenger-side window was having trouble going back up.

Because both rear door windows were inoperable, I assumed that there must have been some other electrical glitch, such as a bad control module. Well, you know what they say about assuming. I did a little internet research and found that the General Module controlled the locks and windows and that sometimes, the relays go bad and need replacing. I found some relays for the General Module and ordered them for $75. They arrived a few days later.

Replacing them wasn’t as easy as I thought. I had to de-solder the old relays out and solder in the new ones. It was a complete disaster and I made a royal mess of the General Module. The repair did not fix the problem. I had to send the module away to California and pay $200 to get someone to undo the mess I made. When I received the repaired General Module, I installed it in the car and the rear windows still do not work. This obviously was going to require me to step back, simplify my approach, and get back to basics.

So, I removed one of the interior rear door panels. Guess what I found. The window motor was completely unplugged from its power source. The cable on the regulator was cut and wrapped around the mechanism to lock the window in a closed position. It seemed that the window regulator had failed. Some “brilliant” automotive technician at the used car lot decided to just rig the window shut instead of replacing the regulator. When I removed the other door panel, I found the exact same thing. A wave of relief washed over me as I found the issue but I also could have smacked myself for all the money and effort I spent chasing a non-problem. I ordered 3 new regulators, one for the front passenger door, and 2 for the rear doors. I installed the regulators, re-connected the motors, and everything worked like a charm. What a goofball!

I know that ditty was a little long, but I wanted to illustrate how we can create our own problems and over-complicate things.

Finding the problem

The system that controls and runs your power windows is a really simple system. Its made up of a few on/off switches, your battery, and a 12 V motor in each door. There is also a mechanism called a regulator in each door. The regulator can either be of the rack, sector, or cable drive variety. That’s about it.

First things first. Is it all of the windows or just one window that won’t function? If its all the windows, make sure the main window lock isn’t engaged. Next, you need to check the circuit fuse. To do that you need to find your fuse box. Your vehicle may have several fuse boxes that control all of the vehicle systems. Consult your owner’s manual or vehicle service manual. Locate the fuse that controls the windows. Fuses can blow if they are old or if a faulty motor creates too much current on the circuit. Pull the fuse, check to see if it is blown.

How do you know if the fuse is bad? If you look closely at the fuse, you will see a metal filament. Usually this filament is curved and shaped like the letter “S”. If the fuse is bad, this filament will appear broken and charred. Replace the fuse and you have fixed your problem. If the “S” isn’t broken and nothing appears burned, the fuse is good and it is not the cause.

Since the fuse is good, let’s go further. Turn your ignition to the run position but don’t start the vehicle. Push the window button. Do you hear the window groaning or do you see any movement or shaking from the window? If you do, there is a mechanical problem with the window. We’ll look closer at that shortly.

If you don’t hear anything at all, there may be a loose, corroded, or broken wire somewhere in the circuit. Start at the fuse box and trace the wire to the window switch. You can do this with a voltmeter or a 12 volt test light. If you have 12 volts going into the switch, but no voltage coming out of the switch when you press the button, the switch is probably faulty. If 12 volts is coming out of the switch, then the problem is either in the wiring from the switch to the window motor or the motor itself.

Let’s look closer, shall we?

It’s time to look inside the door. To do this you need a set of non-marring plastic tools. You will use these to pry the interior door panel from the door once you have removed all the screws from the panel. Some screw heads are hidden in recessed holes or behind little plastic covers. Just carefully pop them out. You could also use a flat-head screwdriver for prying, but I recommend that you wrap it with tape or a rag so that you don’t scratch or damage your nice door panel.

Once the door panel is removed, the problem may be quite obvious, as it was in my case. Your door may have a vapor barrier or plastic sheet that is glued to the door. Carefully remove this. In most cases, you can reuse the adhesive for the barrier during re-assembly. Make sure the motor is connected. Look for burned wires or obvious damage. If everything is intact, you need to test the motor. The best way to do this is to run a jumper wire from the positive terminal of your battery to the positive side of the motor to see if it jumps to life. If not, the motor needs to be replaced.

Mechanical problem

Sometimes the weather stripping or window channel is torn and falling apart. This can jam the window or prevent it from moving the way it should. Also look for objects that might be jammed into the window path. There may be too much friction between the glass and the channel. You can lubricate the channel with silicone spray.

The most common problem with electric windows is something mechanical. The culprit is usually the regulator.

Before you begin to remove the regulator, pull the circuit fuse so that the motor won’t start when you least expect it. To replace the window regulator, you must first disconnect it from the door. You’ll see several nuts on the door that need to be removed. You also need to disconnect the glass from the regulator. This usually involves a nut and a plastic glass holder. Sometimes the glass holder will be broken and has to be replaced with the regulator.

The window motor is usually attached to the regulator by several bolts. The entire regulator/motor assembly needs to come out of the door. This may require some creative maneuvering. Once the regulator is removed from the door, take the motor off the old regulator and attach it to the new one. Reinstall the regulator/motor assembly. Reconnect the power, reinstall the fuse, and test your work. Re-glue or repair any gaskets that are below the top of the door to prevent leaks.

Here’s the recap

1. Make sure the window lock isn’t on

2. Check the fuse

3. Press the window button and listen for groaning or buzzing

4. If all is quiet, look for broken or corroded wires from fuse box to window switch

5. Trace the wire looking for 12 volts

6. If you hear groaning or buzzing, remove door panel to inspect assembly

7. Test window motor, if bad, replace

8. Look for debris in window path

9. Remove fuse and replace window regulator

10. Reassemble and bask in the sunshine of your work

When diagnosing any problem, start with the easy, obvious solution.

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