Window regulator, Window motor

Toyota gear-drive-type window regulator

The mechanism that moves the window up and down is called the window regulator. In cars with power windows, the window regulator is powered by an electric motor, called the window motor. In some cars, the window motor comes with the window regulator as one unit; in others, the window motor can be replaced separately. 
There are two basic types of window regulators: the gear-drive type (in the photo) and the cable type (see photo below). 
In a typical sedan, there are four window regulators; one inside each door. In some convertibles, a separate window regulator can be installed inside the rear quarter panel. A window regulator doesn't need any maintenance or adjustment. If it fails, the failed part or the whole unit must be replaced. 

Ford cable-type window regulator

Window regulator problems

Problems with window regulators are common. A broken window regulator cable can cause the window to jam or fall down inside the door. In cold temperatures, the window can freeze in closed position. When the window switch is operated down, the window can separate from the window regulator. If this happens, in some cars, the window can be re-secured without replacing parts, in others the window regulator might need to be replaced.

Symptoms of a bad window regulator

- the window falls down inside the door
- abnormal noise when a window is moving up or down
- the window rises slow, jams or doesn't close fully
- the window slides up or down crooked
- the window doesn't move at all while all other windows work
- when the window switch is pressed, the window motor runs but the window doesn't move.

How the window regulator is diagnosed

Before deciding on a repair option, the problem must be properly diagnosed. Your mechanic may have to take the door cover off and check what part has failed. If the window motor doesn't operate at all, while other windows work, the window motor electric circuit must be tested to isolate the faulty component. It could be a bad window switch, problem with the wiring or connector or a bad window motor. See how the window motor is tested below.

Window regulator replacement

Replacing the window regulator is not very expensive ($50-140 labor, $40-$180 part) and aftermarket parts are often available. As a DIY project, the window regulator replacement rates from 5 to 7 on the scale from 0 to 10, 10 being the most difficult. You might need to enlist one of your friends to help, as the glass needs to be held in the top position while the window regulator is replaced. It's also very common for door cover clips to break whenever the door cover is removed. You may want to order a couple of new clips. Typically, there are 8-10 clips holding the door cover. In many cars, the power window must be reset after the window regulator or window motor is replaced or the AUTO-UP function will not work. You can google the specific reset procedure or check the owner's manual for your car.

How the window motor is tested

In this car, the window motor in the right front door stopped working. Pressing the window switch up or down does nothing, however all other windows work. We checked the service manual that says to remove the interior door cover and check for battery voltage at the window motor connector.

The manual says to operate the window switch and check for the voltage at the connector. When the window switch is pressed "Down" the multimeter measures 12 Volts, so we know there is power at the window motor switch.

When the window switch is pressed "Up" the multimeter shows -12 Volts, because the polarity changes when the window switch is moved from "Down" to "Up" position.

Next, the service manual asks: does the motor operate by connecting the battery voltage directly to the motor? We did it and nothing happens, the window motor is bad and must be replaced.

The window motor comes together with the window regulator as an assembly for this car. The new part was less than $100 and it took around one hour to replace.