I've gone through all the great write-ups on this site and am still scratching my head. I have the three button switch 4WD modfel.

Initial problem. Not going into 4WD. A vacuum gauge attached to the hose going into the vacuum diaphragm showed ~18" vacuum when in 4WD and did not want to release vacuum when switched into 2WD. All vacuum hoses looked good. You can hear the TCCm switching and the transfer case moving when switching modes. Note: even with vacuum and indicator saying 4WD (low or high) there was no engagement. TCCM flashed code 1. Range of motion for the actuator cable to front axle seemed limited.

I sprayed the cable with with penetrating oil and changed the vacuum switch. Now I have no vacuum at the diaphragm. I've tried two switches and same result. TCCM self tests and no flashing lights => no codes. Still hear TCCM and encoder motor operating.

I applied a vacuum pump to the lines at the switch and found one that holds vacuum with no leak to the diaphragm. With engine running one of the others has ~18" engine vacuum. I'm not sure where the third line runs to from the switch. Help still appreciated.

Thanks

 

I've decided the third vacuum line is the vent. There is no vacuum leak in the hose between the transfer case and the vacuum diaphragm (tested with a vacuum pump). I found a tear in the old diaphragm and replaced it with a known good unit.

After application of penetrating oil the cable moves freely between the diaphragm and the front axle.

I replaced the transfer case motor since I could find no remaining electrical or vacuum problems and no codes and no vacuum to the front of the vehicle. Now when switching between 2- and 4-WD you hear the TCM module click, the TCM motor engage and the front drive shaft engages and disengages.

The vacuum guage shows a slight twitch when engaging 4-WD, but that is it. Still no vacuum to the diaphragm. Further fiddling shows that the leak is bewteen the vacuum switch and the three hose connector. It is pushed on all the way, but not making a good seal on the line to the diaphragm. Has anyone seen this before?

 

Were it goes from the normal size hose to a 1 - 2 inch long larger size that connects to the diaphram? I'm speaking of under the diaphram itself.

 

I havent seen it before but I saw on a website, maybe this one where the guy wrapped the nipples with duct tape and the vacuum lines fit tight.