im working on a 1999 4runner with my cousin and the 4 wheel drive wont engage when we push the 4x4 button a loud clicking is heard and we cant move forward in drive can anyone help me thanks

 

stick or auto? im assuming auto. also motor 3.4?

 

yes auto and 3.4

 

I have a 99, 3.4, auto and had a similar problem. Mine would only engage under 20 mph. Turns out one tire that's even slightly different causes havoc on the system. In my case it was the same size tire, different tread.

 

There are two parts to this system; one is in the transfer case, and one is in the front differential. Due to my entire Vacuum switched front diff missing, I recently installed a Relay that takes care of this issue. I'm planning on scanning in the electrical diagram and detailing what I did to fix this issue. My result is that my 4wd with a SAS works as though it did in the stock condition. I have no flashing 4x4 light conditions, nor do I have an ABS sensor issue, nor any engine light issue.

To address your issue, i suspect you are having a problem with the sensor in the front diff. Or, the vacuum for the front diff disconnect is not working. This needs to be working in order for the 4x4 to be engaged.