I am buying a 2004 duramax 4wd and am wondering about the 4wd selector operation. Owner was not available when i test drove. When i push 4wd high the light blinks a few times then stays steady. When i push 4wd low the light just blinks. I am trying this from 4wd high. Can someome tell me the correct operation of the switch and should the low light stay steady lit in 4wd low?

 

you need to be in neutral to go from 4hi to 4lo, may need to be rolling just a slight crawl too or the 4lo light will just flash and not engage.

 

transmission must be in neutral for low range shift and light will blink then go solid...you should feel it too..

 

yup trans has to be in neutral before it will shift to low range or back to high range, its best to just barely be moving to help it engage easier or else you somtimes get some pretty loud noises as it shifts ,which is also normal.its normal for the light to blink a few times as it is engaging 4x4, then once its steady lit that means its ok to go. you can go from 2wd or 4 high to 4 low, and back either way. you dont have to do a sequence. 2wd to 4hi you can do while rolling down the road at any given speed (just not extremely high speeds)

 

Was the owner unavailable just that once? Generally, this is not a good sign.

A little suspicion now can save you a world of grief later...

 

donno about 2500, 1500 manual says to have truck at less than 15mph to go into 4lo.
btw, before you test it, make sure you know proper 4lo disengage procedure. on mine, have to push several buttons same time. or you'll get stuck in it.
it's nasty. will be very noisy. 4lo.