More 4X4 - Plus Air

I am new here and have read a few of the threads about the 4X4.

I want to try and fix this myself this time as 3 yrs ago, it cost me $1000. At the time, the 4WD buttons would not work at all. I believe they replaced the module under the passenger side dash and also on the transfer case itself.

Now it is doing pretty close to the same thing.

I have the "Auto 4WD" - 4WD HI - 4WD Lo - 2Hi buttons. If I select "Auto" it will appear to engage. However, if I am driving in "Auto 4WD" and start to go up a hill or try to pass someone, the light will blink and it will change by itself back to "2HI". It does this if in 4WD also.

Also, when I go up a hill, or press the pedal hard, it is like I opened the air vents. Air starts blowing in the cabin until I am on level ground again, or back at a cruising speed.

From the threads here, it seems that I could replace the module under the dash, but I just want to confirm. Also, does anyone know the cost of this?

Also, any chance that this could be a problem with the PVC valve?

Thanks and Merry Christmas!

First of all you need to specify a year model here. I assume it's a 98 or newer considering it has the auto 4wd feature. The first thing i would do is disconnect the negative battery cable for about 10 minutes. This will reset your transfer case control module. (tccm) If it works after that you probably have a failing tccm. Also check all vaccume lines.

Now as far as air coming through your vents. Air will flow a little fast but not much faster when you speed up due to a little extra pressure on the front of the vehicle. This should not be related to your 4x4 problem.

BTW, welcome to AF.

It is a 2000. Sorry, I thought I put that in there before.

Anyway... Both problems were due to a cracked vacum hose. It was the bottom hose on that little vacum switch mounted to the firewall on top of the engine (right in the middle).

I just cut off the cracked area and now 4wd is working well. The inside vents are working correctly now too.

You should replace that entire section of hose (actually all the hoses) because now that they're dry it's just going to continue to be an issue

Yes, I will probably do that once it warms up a bit, or at least stops raining.