4WD Vacuum line loose

West Union, OH

#1 Jan 17, 2011
I have a 1999 chevy trailblazer and there is a loose vacuum line that is about 6 inches long lying behind the fuse box. I can not find where this hooks on to. It is for the 4WD. Sometimes (rarely) I can get it to kick into 4hi but most of the time it will not. I have a friend who works for chevy who said it is because that line is off and is not getting enough vacuum to engage the 4wd most of the time. He does not have the time right now to come and look at it till the end of January since he is on vacation with his family and I really need 4hi again before it snows! Any ideas on where this line hooks?

Since: Feb 11

Alliston, Canada

#2 Feb 13, 2011
sorry, but your friend is wrong, there are no vacuum lines for the 4WD system inside the cab of your truck.

it'll be for your enviroment controls, likely the vacuum diaphram that is located to the right & above your gas pedal.

as for your 4WD not working properly....will it go into 4LO without any issues? if so, then it's your TCCM (Transfer Case Control Module) located behind your passenger kick panel. if you have ever had any water leaks over there (actually quite common for these S-series trucks) then it could be shorting out, or simply just worn out. quite common for these trucks as well (i keep 2 spares on hand myself).

Ashburn, VA

#3 Feb 20, 2011
It will not kick into 4hi or 4lo at all with that line off. I made a mistake on where the line is laying. The line I have found loose is laying behind the brake booster box under the hood, not the fuse box(meant the one under the hood). I know this line is the problem as I wrapped it up with electrical tape so it is closed off completely and my 4hi and 4lo will work this way but I can also tell my brakes seem a little on the weak side. I am assuming this hooks into the brake booster box somewhere but I am not sure on that. I am just trying to find someone now with the same style blazer with 4wd to look and see where this line attaches to.

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