Hi, I'm new to the site, nice forum you got here. Hoping I can get some answers for the problem I'm having. Recently bought a 99 Blazer 4x4 for my wife to get around in the winter since she has a camaro. Got a good deal on it and it's in great shape and runs like a champ. Problem is when i went to push the button to go into 4wd, you can hear it click but doesn't lock in. And when you go back into 2wd, the same thing, a click sound. The main reason for this purchase was the 4WD, now I'm a little disgusted. I'm hoping it's nothing major, I just don't know where to start and can imagine what it would cost for a garage to fix it, was hoping I could do the repair, just don't know what it could be. Any information would be greatly appreciated. Ken

 

Does the switch on the dash have 3 buttons or 4? Where do you hear the click? Can you hear the transfer case try to shift, (more of a clunk sound)? The transfer case control module, (TCCM) is located behind the passenger side kick panel, (to the right of the passengers feet). The electrical connector is known to accumulate corrosion on the terminals. Take it apart, clean it with carb spray, Q tip, compressed air, etc, and plug it back in. Could be a problem with the dash switch, or the encoder motor on the transfer case, the vacuum switch on the center of the firewall under the hood, the actuator under the battery tray. There is a thread here in the forum titled "4wd no worky" and it might help.

 

It has 3 buttons and the click sound is coming from underneath. I don't hear a clunk sound that I'm aware of. So this is something common with this year Blazer? I won't have a chance to work on until tomorrow, my son's Blazer has a fuel line leak and I'm trying to get those replaced today, so that will be my project for tomorrow. Do you know what the worse case scenario would be? I will look for that thread you mentioned, thank you for the information, I really appreciate it. Very frustrating day. Thanks again!

 

If you hear something, it probably the T-case switching in the front diff, but sounds like the front axle is not locking in.
This is done via a vacuum actuator that is located under the battery tray, or you can remove the skid plate and look up under the battery.

Common problems are:
The actuator diaphram is torn and thus not pulling the cable that locks the front axle in.
Leaking vacuum lines under the hood not supplying vacuum to the actuator.

Check all the vacuum lines under the hood, especially at the driver's side, near the firewall. There are a couple of of "T"s and elbows...check all the lines. If any leave a black residue on your hand, replace it....or replace all of them...one at a time.

Does the 4x4 buttons stay lite when 4HI selected or does it flash and go back to 2HI?

 

When I push the 4HI button, it stays lit and doesn't blink. I'm going out to try to look at it now. Thank you again for all your help. I will check all that was mentioned for this thread. I hope It's an easy fix, but knowing my luck, I'm afraid to even look.

Another issue is the heat don't work. It blows out cold air, I just bought a thermostat, hoping that will fix the problem. Figure I'll start with the small things first. If it would happen to be the heater core, is that a pretty long job? I would hate to pay a garage bill, cause it is something I could do, I just don't know how long of a job it would take, I only did it a few times on older vehicles. Thank you.

 

Raise the right front wheel off the ground. With the engine at idle, trans in park or neutral, select 4WD. The right front wheel should not turn by hand.

Heater: Does the vehicle have automatic climate control, or manual HVAC? Engine at operating temp, (198F) both heater hoses at the core must be hot to the touch with bare hands. If both hoses are not hot, the core is restricted. Very common if the cooling system is not flushed every 3 years/36K miles. Removing the hoses and flushing the core with a garden hose, (both directions) usually helps. Replacing the core requires the removal of the entire dash and heater case. If you haven't done one, plan on ~8 hours, and you'll need an assistant for part of the job.

 

I removed the battery box and the vacuum line was on, I pulled it off and pushed it back on and it looked a little rusty so I oiled it all up and moved it back and fourth a few times and now it works great! Thank you all for the advice, you saved me a lot of time and money.

As for the heat, I only got to change the thermostat and that didn't help. I'm going to do what Captain Hook said and try flushing the core with a garden hose and see if that helps. It seems that the core may be blocked, I hope thats all it is. If that don't work, any other small steps before replacing the core? Again I can't stress enough how thankful I am for all your help!

 

Automatic climate control or manual HVAC? Are both heater hoses hot where they connect to the core?

 

I'm pretty sure it's a manual. When I get home from work I'm going to try blowing it out with my air compressor, hopefully it will clear out, if not, I don't know what's next. I'll check the hoses today too and let you know. Thanks again.

 

Would not recommend using compressed air....tiny passages and high pressure air and the core will leak for sure.
Just use the garden hose method and reverse flow. You will be very suprised at how much junk comes out....unless it is so blocked that replacement is needed.

And then you are in for a job.....actually just need to remove the dash. Alot of work, not difficult, just need to take notes as to where bolts/screws go.

Good luck.