just got this car a few days ago, its a 2002 Blazer LS with 63000 miles and the 4 button 4wd system. So here's my issue when I try to engage 4wd hi or the 4wd automatic the yellow indicator lights just flash indefineately and never get solid as they are supposed to. No "service 4wd" light on the dash. When I hit the button I can hear it clicking or something. I have done some searching and it seems with these symptoms the most common solution seems to be a vacuum hose issue, does that seem right? I am wondering where the hoses are and where they tend to get damaged or come loose from. sorry for my ignorance this is my first 4wd vehicle.

also I have read about some control box on the transfer case can go out causing similar issues and to check the connections on something in the passenger side kick panel? does anyone happen to have a picture of where these things are located and what they look like so I don't start fideling with the wrong thing by mistake. again sorry for my ignorance. thank you.

 

I just bought a 2001 blazer LT with a four button 4wd. Same thing lights on auto4 and 4wd just flash even though I hear clicks behind glove box. Under the hood above the distributor is a small solenoid with two vac hoses connected. One hose connects to the engine and has constant vacuum. When it's in 2wd, the solenoid is closed and no vacuum goes to the other hose. In 4wd you can feel vacuum at the other spigot on the solenoid. This hose goes to some kind type of cable pulling thing under the battery. This is as far as I have gotten because it's cold out and I haven't gotten down to look under to see if the cable is being pulled. I think there is a switch on the transfer case that needs to engage. Some where I read that you can check this by trying to turn the front drive shaft by hand with 4wd engaged. When it warms up I'm going to try that.

 

hey thanks for the info gives me a place to start with the vacuum hoses. I read about the actuator under the battery too, what is the test to ensure it is functioning properly. I also read about trying to turn the front driveshaft, however felt kind of silly because I looked under the car briefly and did not see the front drive shaft. I saw the one that powers the rear wheels, but did not see the front one.

 

I am having a similar issue with my 98 Blazer that just started recently. I push the button to switch it into 4 HI or LO and I can hear the click from the button and the button stays lit, and hear and feel the transfer case trying to engage the 4wd but it does not feel like it is engaging. The service 4wd light is not on. It has been too cold here yet to get out there and look around to see what it could be.

 

I checked the front drive shaft and it did not move indicating 4wd is engaged. But when the 2wd mode was engaged the drive shaft would not turn either, is that normal?

 

Yes, that is normal for the NV236 (4-button) transfer case. The front driveshaft will turn given sufficient motivation. The front output is powered through a preloaded clutch so even when it is in 2hi, you have to overcome the preload on the clutch pack to turn it.

When you attempt 4HI, Auto4, or 4LO, does vacuum flow to the front axle engagement actuator located under the battery? If it does, is the cable being pulled 1/2" to 3/4"? If the TCCM isn't seeing the front axle engage, it may dump back to 2HI.

You can try to scan the TCCM for codes even though the service 4wd light is not on. It may have something pending.

 

fixed...the vacuum hose was not attached to the actuator , hooked it back up and the 4wd system works flawlessly now. Thank you for the help.

 

Gotta love the easy fixes! Glad you got it fixed!