Do you have the Auto4wd function? If not, have you followed through the diagnosis chart in the DIY section?

 

Any update on this problem Bob? If you get a chance, could you let us know if you have the Auto4wd option? If you don't, have you checked out the DIY article on OBD2 Non-Automatic Transfer Case Diagnostics

 

I'd be curious what Bob (and anyone else with the Auto 4wd transfer case) came up with on this...
Recently my 2001 LT 4x4 with the Auto4WD started doing something similar, won't engage 4HI or 4LO, just blinks. 2Hi is fine. I do get the loud "clunk" sound when I put it in 4LO while stopped in neutral, but I know the front wheels are not engaging because I can't get the blazer to go up car ramps on cement without the tires pushing them front. I changed the transfer case fluid with AutoTrak II, and yesterday I unplugged the electrical connectors to the t-case and front diff, cleaned them, coated with di-electric grease and reinstalled. I also tried removing, cleaning, reinstalling the control module in the kick panel, no luck. I guess the next step will be to pull the battery and look for the vacuum actuator under the tray. I've also not tried to put it in 4LO and see if the front driveshaft locks, that will also be something I'll try next. Any other suggestions?

As a side note, I had bought one of those AutoTap computer readers, I was disappointed to see it only reads the main computer, and doesn't seem to access the ABS or t-case stuff, at least not that I've figured out anyway...

Terry

 

Terry if it's auto 4wd (rpo NP8) it has an electrically controlled vacuum solenoid mounted almost dead center of the firewall above the distributor, that switches vacuum to the actuator under the battery. Pull the connector out of it and put a test lamp across the 2 terminals (DON'T DAMAGE THE TERMINALS!) with the key on hit your 4HI button and see if the test lamp lights....if so then you know it is either a vacuum problem or cable/actuator problem. If the test light doesn't light...then you are not getting the signal to engauge the front axle from the TCCM.

 

So that's what that vacuum solenoid is for... thanks for the info Bill! I ran out and checked it in the dark, didn't start it but just put it in RUN and hit the 4HI, I get 12 volts at the connector. It's looking more like either a vacuum or cable issue. I'll have to dig out my vacuum gage and check the actuator side of the vacuum line, that should tell me if the vacuum switch actually opens and if there is a leak before I go to pull the battery and the tray.

Thanks for the help!
Terry

 

No problem Terry..any updated info yet?

 

Update...
I found out the vacuum solenoid was stuck... when I wouldbypass the solenoid by connecting the two vacuum lines together, 4x4 would shift in and out just fine. I took the solenoid off and bench tested it, sure enough it wouldn't open. Then for kicks I reversed the polarity of the 12 volts and to my suprise that "unstuck" the solenoid. I actuated it several times, seems to be working. Installed it back where it came from, and I was able to shift in and out of 4wd with no issues. I'll have to keep an eye on it to see if it sticks again. I would guess that this is a dealer-only part, so I'll wait for it to fail one more time then I'll replace it.

Thanks for the help Bill!

Terry

 

No problem Terry, glad we got it fixed before the snow starts flyin'!