When Repairing Window Master Switch for GM, you have to realize that GM power window switch is a stand alone design when compared to other domestic vehicles. On the GM lower end vehicles, the driver master switch controls all the power window motors in one location. Power to this master power switch comes from either a fuse or power relay or body control module (BCM). When using the master power window switch, it cycles power and ground supplies to your power window motor.

There is no polarity to the window motor so one moment, the wires used by the master switch could be positive and negative and using another button, it will reverse itself to operate the motor in another direction. In contrast, passenger door switch is basically an on and off switch to run the power window motor in either direction. The rear window switches are identical in design as the front passenger switch. Most GM power window electrical system were made into this configuration (except the high end ones) until the introduction of power window modules in 2003.

The power window module is actually a computer masquerading as a power window switch. It has more added features and could work independently without a body control module directing it. Besides having a logic system to reverse the grounds, it can run 2 power windows in different modes; automatic shut offs, interface with the vehicle’s security system including the operation of express up and down mode. On high end vehicles, each door could have it’s own power window module.

When repairing window master switch for GM vehicles with power modules, use the guidelines I gave on my earlier blog:

CLICK HERE to see power window basic test

When troubleshooting power module wiring problems, don’t forget to check the voltage drop for suspected circuits. If you suspect the door jamb wires are the culprit, use a good digital voltmeter to check the voltage drop. Any voltage reading above 0.250 volt will show that the wire or component is faulty. This test can be applied on both power and negative wiring circuits. Repairing window master switch in this manner is a good alternative if you cannot find the faulty wires at the door jamb.

Some high end GM vehicles made before 2002 like Cadillac might come with window power modules. This device is also becoming standard option on newer GM vehicles starting 2005-2006 models.

When faced with window master switch problems with power module issues, here are some tips on how to fix them:

Begin your troubleshooting by getting the BCM code which can start with a letter “B” followed by numerical digits. The B stands for body control system for lightings, keyless entry, climate control and other power accessories. You would need a code reader that could read BCM codes and if possible be able to clear BCM codes. If you suspect that the power module needs replacement, try these:

1.) Try resetting the BCM codes using the scanner or code reader. Some garages are reporting the removal of battery connection overnight to clear the code without using a code reader.

2.) Check with your dealer in case there is a pending service bulletins regarding the power module of your door. On some occasion, the dealer will reprogram your power window module without charge.

When you verified that the power window module is defective, make sure to bring it to your dealer so they can reflash or reprogram it. The power module computer upgrade will also be required if you replace window switch. Without reflashing, the new window power module in your window switch will not work.

Thanks,

Richard

Click HERE if you need online assistance to fix your power window

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