Here's the poop: 01 Blazer LT; 121,754 miles; 4X4. Problem is when I go to engage the 4 wheel drive, all I get is flashing lights. I hear nothing that indicates the axle is trying to engage. It goes back into 2 wheel drive fine.

I have no idea where to begin to check. I have heard about two things that might be the problem, but I wanted to ask here if there might be anything else. The first one is the FRONT AXLE ACTUATOR VALVE located in the engine compartment. The other one was the FRONT AXLE VACUUM ACTUATOR that is supposed to be under the Battery Tray (?).

Any ideas, advice would be greatly appreciated because I am trying to get it ready for trips up north.

JP

 

I had the same symptoms on my '00...I heard nothing either and suspected the transfer case encoder motor. As it turned out I had a vacuum line broke off at the FRONT AXLE ACTUATOR VALVE not sure how this ever could have happened but there it was not connected. Re-connected the line and it worked. Good luck.

 

Ok it has been a year and I am going to tackle this once and for all. Why you ask? I have 20" snow (or did). So now I need some advice. To recap my 4x4 won't engage. When I push any of the 4 wheel buttons they flash. No noise, nothing indicating it is trying to engage. I am going to try to replace the VACUUM ACTUATOR SOLENOID VALVE first. Questions are: (a) how is this bugger installed? Does it clip on or something?? and (b) should I hear a "hiss" when disconnecting the vacuum lines? The attached photo is what mine looks like just mounted upside down.

Is this the same thing as your FRONT AXLE ACTUATOR VALVE? Where did you find the disconnect??

When I tried to remove the bottom vacuum line it hissed like it was either sucking air in or air was escaping. Is this normal? Please let me know as next weekend we are Poconos bound and that usually means more white stuff.

I would greatly appreciate any/all advice or other areas/remedies you may have had luck with. Thanks in advance.

 

What testing have you done to determine that you need to replace the solenoid? The solenoid can be tested using some jumper wires. The control wiring can be tested with a multimeter.

One side of the solenoid will be connected to the vacuum reservoir which is connected to the engine. There is a check valve that stops the system from loosing vacuum when the engine is off. It is completely normal for this to hiss as the vacuum is lost when the line is removed.

 

From everything I have read here on the site, it is pointing to this solenoid. I am not a mechanic but I am prone to replacing those things I can and work my way out until the problem is corrected. I believe there is another item (can't remember what it is called) under the battery tray. Point me in the right direction and I will check it out. . .

 

The part under the battery tray is the vacuum actuator. It's what actually engages the front axle by pulling a cable.

http://i20.photobucket.com/albums/b2...umActuator.jpg

You should be able to see it by removing the left headlight and looking at it through the holes behind the headlight. Have someone sit in the truck and engage the 4x4 while you watch. If it doesn't move that could be your problem. If it pulls the cable a bit then its fine.

If it doesn't move check the black rubber part of it for rips or tears. If there are none then crank the engine, pull off the vac line to it, engage the 4x4 and see if it pulls a vacuum. If not follow the lines back and try to find any loose fittings, cuts, nicks, or other problems that would cause it to loose vacuum.

If there are tears in the rubber part then you can either replace it for about $50 or buy a posi-loc cable (http://www.truckmod.com/directpart.a...tnumber=PSL500) for $200-$300 OR make your own posi-loc for about $30 (https://blazerforum.com/forum/article-submissions-discussions-47/how-homemade-posi-lock-cable-system-discussion-thread-24131/). The last two are great cause you'll never have to fix the actuator again

 

Thanks so much. I will pull the headlight out this week end and see what happens. Hopefully I will find the source of the problem and take care of it. I will let you know how it goes . . . .

 

Ok, here are today's results. Located the actuator. The diaphragm looked good and the cable moved when I manually pulled it. Had my neighbor turn on the ignition and press 4 LO. Nothing. Had my wife get in and start the truck, put it in Neutral, and press 4 LO and still the actuator did not move. I did hear the transmission (?) try to engage but the front end would not engage. I drove it around the block and again in Neutral and put it in 4 LO and it felt like it did go in but the 4 LO button continued to flash as did all the others. I am going over to a friend's shop and we are going to put it up on a lift and have my wife engage it (she is the lightest) and see what happens.

Oh and I pulled the lines off the solenoid and one side was pulling a vacuum. Held them together, had my wife start it, and repeated the process and still flashing buttons. Could it be the solenoid has failed electronically????? Really want to get this fixed this week. Advice/suggestions are greatly appreciated.

More to come. . . .

 

Have you tested anything as has previously been recommended?

 

Hello I have the same problem, but mine clicks when I push the 4 wheel drive button. If you're getting vacuum to the actuator, check the shifting cable, after that check the motor attach to the transfer case and don't forget the module on the passenger side kick panel. have someone push the 4 wheel drive buttom while you check to see if the module is working