I did searched but could not find threads to help me diagnose what problem it is.

So the driver's window do not go down, occasionally. These are what it does:
(1) Every once a while it does not go down from closed position. (like every time you are at a toll or parking lot entrance lol..)
(2) Haven't observed bouncing up when going down or bouncing down when going up.
(3) Haven't observed clunchy/grinding noise when it is operating.
(4) When it does not go down, engage the open window switch can hear the faint 'tick tock'. So I guess the motor is good?
(5) What's strange, when it does not go down, I use the key in driver's door hold in open, all windows work. Then the problem don't come back for a while...

So the motor's ruled out I guess. Should it be the window regulator? I mean if it is, why the key can open the window... Wierd..
Can it be other problem?

Thanks in advance for any suggestions and comments.

 

So what you are saying is, with the KEY, the window goes up and down ALWAYS? EVERYTIME? No problems at all? You only have the problem when using the switch inside the door?

 

Yes that is the case.

It was stupid... But today I checked it very carefully, and found out it's just a faulty switch on the driver's door. The switch close the driver's window correctly, but the contact for the open window side of the switch must have gone wrong.

I will just go to the dealer to buy a new switch assembly and install it. Hopefully it won't be too expensive.

Thanks for the suggestion, I did check and found out the key open and close the window correctly always - which should mean a faulty switch.