I am having a problem with the 4wd on my 2001 blazer. I push the button to go into 4 hi, or 4 lo. The lights blink, hear the click under the dash and then it goes back to the 2wd light. I ran the code test, and no codes came up. I did replace the vacuum switch on the transfer case earlier this summer. It sounded like it was engaging the 4wd slightly all the time. I replaced the switch and never tried the 4wd until this week, when I am having this problem. Could it be something with hooking up the vacuum lines wrong on that switch? Or is this something else that is going wrong?

 

i had this issue with my truck when i first bought it, take off the 4wd actuator on the transfer case and clean up the electrical terminals on the pins and the wires its self some get corrosion in them and prevent them from shifting into 4wd. i cleaned my terminals and never had a issue since

 

If you are hearing the "clunk" after pressing the 4HI button, then the transfer case is engaging. However the problem is that the front right side axle is not engaging...which is why the 4HI flashes and then returns to 2WD.

Suggest first checking the vacuum lines under the hood, especially near the drivers side fender. The vacuum lines cracks and falls apart in this area for some reason.

If vacuum line is good, then check for vacuum after the electrical switch mounted on the firewall when you switch to 4HI. Next would be to remove the battery, battery tray and check the vacuum actuator diaphram and cable. This is what engages the right front axle.

Likely it is a vacuum line leaking, but I had the firewall switch go bad, and of course others have had the actuator go out.

Good luck.

 

I would guess vac leak, find a diagram for the vac lines for the 4wd, search the forum, and check them all. also check the vac switch.

 

Figured out the problem. I tapped on the motor on the transfer case, and it engaged. See how long this lasts before I have to replace that. I heard the click under the passenger side dash, and nothing else was happening. After I decided to tap on the motor on the transfer case, and then it engaged as it should. So far it has been working.