4WD will not engage

gmc
1500

#1

V6 automatic w/ a manual 4WD shifter on the floor not the cute little 4WD button on the dash. When I engage the 4WD the incicator lite on the floor console no longer lights indicating 4WD is engaged and the 4WD system is in fact not engaged. I’ve done some troubleshooting. Associated fluid levels are OK. Operating the floor shift lever applies drive power to the front drive shaft. It appears the front differential does not do whatever it’s supposed to do to transfer power from the drive shaft to the front axle’s. Additinally, there is what appears to be a soleniod on the front differential. Is this true and could this solenoid be defective and not doing whatever it is supposed to do to the front diff to engage the differential / axles. ? ? ?

Thanks for your help.

LouS/


#2

had the same problem with a jeep. I thought it was the solenoid but it ended up being a faulty vacuum line to the selenoid. maybe the problem is similar?


#3

Captain, as they say, the devil is in the details. What year is your truck? They’ve been making 1500s for a long, long time and as you might expect, the front axle actuator design has changed over the years.


#4

It’s a 1998. I was under the impression that there was a vacuum line only to the sutomatic 4WD systems where there was a 4WD engage button on the dash. I guess I’ll crawl under it again and look for a vacuum line.
Thanks for the help. This cartalk web site is turning out to be a great source of info.
LouS/


#5

There is an electrical plug on the transfer case that a cleaning of the contacts many times clears up the issue if that is applicable in your case.


#6

I have a 2000 Blazer with the dash switches. I believe the transfer case is engaged electronically and the front axle is engaged with a vacuum operated actuator. The electric vacuum switch on mine was bad. I was fortunate the switch was mounted on the firewall and easy to replace. Some switches on mounted on the transfer case. The vacuum actuator is under the battery mounting plate.

Ed B.


#7

Now you confused me. In your first post you said you did not have the dash controls. Are you replying to the first responder?

AFAIK, the actuator in your truck is a heated wax pellet actuator and they are known to go out, especially if you put stress on them while actuating. Keep the wheels straight ahead when engaging 4WD…

Here’s a link to a troubleshooting guide- http://www.4x4posi-lok.com/PDFs/TSG_chevyK.pdf