Troubleshooting power windows - No matter the power window design, it still has to open and close the glass. - Motor Age - Automotive training, certification & parts info
Your customer drives up to the tollbooth on a rainy day, rolls down the window to hand their toll to the attendant and then
finds that the window will not roll back up. They try to tug the window into position without success and drive to the closest
shop, frustrated and wet. Ever happen in your shop?
But that's not the only complaint you may face. Other common faults are windows that only move partially through their travel
before grinding to a halt, work in one direction only or no longer respond to their auto up/down feature. A few simple checks,
however, can often quickly and successfully locate the cause of these common problems.
Basic Function
1 Some power window switches are just that — switches. Keep in mind that no power to a passenger window can be the switch
on the problem door or the one on the driver's master switch console.
Power window systems use an electric motor to move the glass via a regulator to which the glass is attached. The motor is
a DC (direct current) design, using two brushes riding on an armature, just like a starter motor. The direction of rotation
is determined by the direction of current flow applied to the motor. The amount of current flow is influenced primarily by
the amount of resistance to movement the motor has to overcome. This is true of any electric motor, whether it be a window
motor, starter motor or even a fuel pump.
2 Some switches are control module inputs and only send a request to the module in charge of actual window operation.
Most power window systems use some type of current limiting device to prevent damage to the circuit should current flow become
excessive. Of course, excessive wear or internal binding of the armature also can cause excessive current and result in intermittent
operation. Ever had one that worked for a portion of the travel, then quit until it sat for a few minutes? Another cause of
excessive current is dirt and debris in the window run — that rubber molding the glass rides in. This causes the window to
be harder to move, especially up, with a resulting increase in current demand on the motor circuit.
3 Cable regulators are becoming the norm, and are frequent causes of window failures on many models.
Current direction is controlled by a variety of switch designs, but they all share one common denominator. When the switch
is placed in one direction, one pole of the window motor receives system voltage and the other is wired to ground. With the
switch position reversed, the poles are reversed and so is current flow. Systems with advanced features like automatic up/down
or obstruction detection often are controlled by a control module. Here, the switch is nothing more than an input signal to
the module, and the module itself takes care of sending power and ground to the motor. In these systems, the module can be
a dedicated module or incorporated into an existing body control module. Check the schematics for the system you are working
on to know how yours is controlled before troubleshooting any electrical issues.
Some regulators are a mechanical design, much like those used on manual window systems. More and more, though, cable type
regulators that use a cable and spool arrangement to transfer the motor's rotation to the window glass are being used. While
they certainly offer lighter weight, the cables are prone to binding in the spool at the first sign of any kink in the cable,
and often break away completely from the window plate. This usually results in a window that can be freely moved up and down,
and you can hear the motor itself running with no effect on the window position.
4 Several makes, mostly European, attach all the window components to a modular base. Replacement is more involved, but not
difficult.
Don't rely on this quick check alone. The plastic gearing, internal to the motor or where the motor meets the cable spool,
can strip and result in similar symptoms.
Pete Meier is an ASE certified Master Technician and sponsoring member of iATN. He has over 35 years practical experience as a technician and educator, covering a wide variety of makes and models. Now, as technical editor for Motor Age, his primary goal is to bring working technicians the information they need to succeed.
Articles by Peter F. Meier
post a comment
Dental Lab Products | E-NewsletterShare This Page:
