Two thoughts, does this have 'express' or auto-down? That circuit
might be interfering with the operation.
As well, there may be an overtemp protector on the motor that opens.
The protector (a very simple thermostat) may be defective, or more
likely the motor is really overheating. One test would be to open the
door panel to access the motor, and drop the window. Then (carefully)
check to see if the motor is hot. If it is too hot to hold your hand
on it, then I'd say the motor was dead.
From that stage put a meter across the motor leads and check voltages.
Window motors are reverse polarity in most vehicles, check to make
sure the motor is always getting voltage.
GM products are infamous for this window motor problem. It has been going
on for YEARS.
A new motor is almost certainly needed, as Harry says.
When you take all this crap apart, look for places in the grooves where the
window can be fouled, fabric deteriorating in those areas, etc.
Lubricate where needed.
This is another case of GM knows about it, and doesnt give a shit. Other
cars, for the most part, dont have this sort of LONG term problem.
You ought to see the ones in late 1980s Buick cars. I have to start both of
mine if I want to put the windows up, otherwise it just won't happen.
I haven't attempted a fix yet, but it would not surprise me to find that the
switches have either oxidized or burned. The motors are cheaply made, but I
can't see anything obvious about them that would result in their running
slower as they age. I have given some thought to also pulling them out and
cleaning the internals after repacking the bearings with fresh grease. How
much of that I do depends on how serviceable of a design the motor is.
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