Monday, July 22, 2024 Detailed Auto Topics
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Power windows are convenient, until they malfunction. When the window stops working in an up position, it is annoying. A power window that will not close may be even worse, especially in the cold or rain. Diagnosing the problem with power windows is easier with a systematic approach.

All windows quit working simultaneously

When a power window fails to operate, a short checklist helps to narrow the possible causes. If all windows stopped working at once, a loss of power to the system is likely. Many systems use a single relay and power supply for all windows. When all windows quit working simultaneously, first check for a blown fuse or bad relay.

Our Detailed Topic, Checking fuses and relays, gives details on how to best check for a bad fuse or relay. If all fuses and relays are good, we next check for power at the driver door master-switch. Often all power runs through this one switch and failure will stop all windows from working. We will need a wiring diagram for the vehicle to identify the various color codes they use. Without such a diagram, testing the switch is nearly impossible, but we can make sure at least one lead has power, when tested to ground.


Pulling fuses out of the panel to check them is less effective and can cut power to keep-alive memory needed by the various modules in the vehicle.  It is easier and more accurate to electrically test fuses in place.

Power window lock out switch

Many power window systems have a lock out switch.  This switch may cut power to all but the driver's window, to avoid anyone controlling them without permission. Always check to see if there is a switch that locks the power-windows out.  Often we may accidentally push the switch and not realize it. It is embarrassing to learn we have depressed the lock-out-switch, after bringing the vehicle in for service on the power windows.


Windows that have remained in the up position for several months will sometimes stick in the rubber guide. A window cleaner sprayed in the crack between the glass and the guide may free the window.


One window will not open or close

It is not likely that a fuse or relay will cause a single window to not roll up or down. More likely, the power window motor, door switch or window regulator has failed. Looking for symptoms helps guide us to the most likely cause.

No sound coming from the door, when we press the power window switch, suggests a bad motor or power is not reaching the motor. Hearing the motor running, without the window working, usually shows the power window regulator or clutch are bad.


Try the power window switch at the individual door and the master-switch at the driver’s door, when a window fails to roll up or down. If one switch works, and the other switch does not work, we know the motor and wiring are good. This most often suggests a bad power window switch.

Before we can test

To gain access to the components of the power window system, it is normally necessary to remove the interior door panel. Vehicle makers use several methods to attach the panel to the door frame. Our detailed topic on removing interior door panels gives several details. Be sure to learn how to remove the panel, before preceding.

Testing the power window motor

Checking the power window motor requires us to remove the door panel. Each vehicle has a unique attachment method, but carefully prying the panel from the door removes most.

Back probing an electrical connector

With a digital volt meter, we can test to see if power reaches the window motor. If the power window motor has two wires, it is an analog system. We can back probe the connector at the motor, to detect if current flows when we press the switch.  Please review our article on electrical testing for details on properly probing a circuit. Front probing a connector or piercing the insulation is bad practice and often leads to other problems in the future.

Power window motors, with multiple wires leading into them, are digital and professional diagnosis is best. With analog motors, checking between the two wires should show either 12 volts or -12 volts, depending on the position of the switch. Full current available and a motor that does not run suggests a bad motor.  A lack of current flow means power is not reaching the motor and the problem is upstream.

Voltage drop testing

Finding current at the motor, below system voltage, suggests high resistance in the circuit. Voltage drop testing is handy for finding the source. For example, voltage at the motor side of the connector may read 11 volts, with the switch turned to on. If system voltage is 12 volts, we have resistance in the circuit. This may cause the motor to run slowly or not at all. High resistance can also cause repeat motor failures.

Checking for high resistance in a connector with voltage drop

We test for a voltage drop by back probing across the suspected source. Voltage drop testing is always done with the circuit, under a load. Finding a voltage reading that is above 0.1 volts shows high resistance in the circuit. We should remove and inspect the connector for damage, corrosion or a poor fit. The technician can repeat the process until the problem is found.

Power window motors today are better than they were just a few years ago. Permanent-magnet electric-motor technology greatly increases the reliability. These window motors are very small yet powerful. The window motor normally rotates a worm gear attached to the motor armature. This worm gear turns a driven gear at a 90-degree axis.

Window motor drive clutches

Window motor cutaway showing worm and drive gear

The driven gear attaches to the regulator-drive gear, often using drive rollers. These rollers allow for any slight misalignment, smooth window travel and quite power window operation. The rollers can also become brittle and break. When the drive rollers break, the motor will run, but the window will not go up or down.

The regulator drive gear and rollers 

If we see that the regulator-drive gear does not turn, with the motor running, the likely fault is with the drive rollers. We can often replace drive rollers at a much lower cost than the window motor. This is particularly true on many older Ford products.

Testing analog power window switches

The power window switch in the at rest position

When we are not using the power window switch, it is in the rest state. This means that no current will flow to the motor on either wire. If we check the connector at the motor, neither lead shows current when we check to ground. Both leads may show continuity to ground, depending on the design of the switch.

Power window switch in the lower or down position

Pressing the switch to lower a power window, directs current to one wire and grounds the other wire. Direct current flow in this position causes the motor to rotate and lower the power window. Back probing the connector will show 12 volts between the two wires and -12 volts if we reverse our test leads.

Power window switch in the raise or up position

To raise the power window, we push the switch in the opposite direction. This reverses the polarity of current flow within the switch. In other words, the terminal that has 12 volts in the lowering position, has become the ground in the raising position. The lead that grounds the motor when lowering the window, becomes the current source when we raise the window.

By reversing the current flow to the motor, we cause it to rotate in the opposite direction. Turning one way will lower the window and rotating in the other direction will raise the power window.

The motor turns, but the power window does not move

Gear drive window regulator

Converting the rotation of the motor into vertical window motion is the task of the window regulator. In the past most regulators were usually gear driven with arms. Small wheels roll in the tracks and the arms push the window up. This is a parallelogram design. These regulators were robust and gave very little problems. They are also a bit heavy and expensive to build.

Cable type window regulator

Most manufacturers now use cable type regulators. With the cable regulator, the motor drives a wire cable though the mechanism. A series of plastic pulleys guides the cable. A regulator carriage attaches to the cable and to the window glass and slides on the regulator track.

This system is light and cheap to produce, but is also fragile. Broken cables and pulleys are common. Cable regulators are not repairable and we must replace them as an assembly.

Replacing the window regulator

The regulator normally attaches to the door shell with special rivets. To replace the regulator, we drill the rivets out. After we replace the regulator, we use a riveting tool to replace the rivets in the door and window glass.


Purchasing replacement rivets from the OEM supplier is best. Many rivets look alike, but can break the glass or come loose if they are not proper for the application.


Using bolts to replace the original rivets does not usually work. The bolt may stick out and jamb in the mechanism, causing a repeat failure. Bolts also do not supply the proper tension that engineers design into the special rivets. Always use the same attachment method the manufacturer of the vehicle specifies.

Cleaning the power window tracks

Window regulator mounted in door shell

Felt and rubber channels guide the glass up and down in the opening. Keeping these channels clean and occasionally lubricating with dry silicon spray greatly reduces wear to the motor and window regulator breakage.  If the channels get too dry or sticky, the window glass may refuse to move.  Cleaning and lubricating the channels with dry silicon will sometimes restore window operation.

Power window repair is a bit tricky and many folks prefer to have it professionally done. AGCO can diagnose and repair any power window issue your vehicle may have. AGCO, it’s the place to go.

For more tips on preventing power window problems see our Detailed Topic, Avoiding Power Window Problems.

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