I have a 2000 2 door with the 4 button switch on the dash. I have been having problems with the switch not indicating any mode, all lights are out, then come back on. I'm pretty sure that its a vacuum problem, but I can't find the vacuum switch on the transfer case. I did find the vacuum actuator solenoid on the firewall. Is this the only switch, or is there still one on the transfer case? any help would be appreciated.

 

A vacuum problem would not make all the lights go out. A vacuum problem makes the lights (4HI, 4LO and Auto4WD) blink. The vehicle will shift in and out of 2HI to 4LO only.

Sounds like you have an issue with the TCCM. Most likely corrosion in the wiring and grounding points.

 

4 button, (Auto 4WD) does not have a vacuum switch on the transfer case, firewall only. If the lights are blinking, it's an electrical problem. First place to check is the transfer case control module, (TCCM). It's located behind the passenger side kick panel. Remove the TCCM and the electrical connector and check for corrosion on the pins. Clean it up if necessary and put some silicone dielectric grease on the pins/connector.

 

I'll give you another scenario: the four-button switch on the dash could be failing. My wife's '00 Blazer had the same problem with the lights going on and off. I replaced the dash switch and everything functions properly. Check the dash switch before you take out the TCCM.

 

Thanks for all the info. I changed all the vacuum lines (that I could find) yesterday, & it seems to be working better, although I am still having light issues. I can hear the TCCM clicking, when selecting different modes, so I think the switch (which is a lot cheaper) may be my next move. I am also going to check the harness & grounds on the TCCM. Thanks for all the information.

 

My '02 2wd indicator lite would not always come on and required a few taps to the switch in order to get it to come one. And going into 4wd was slow; I took the 4 button switch out of the dash, took the switch housing apart to expose the circuit board, re-flowed the solder on all the connections and put all back together.

Now the 2wd lite comes on everytime and vehicle now goes into 4wd mode very quickly...like it is supposed to.

So I suggest taking the switch out and reflow all the solder connections. The switch housing just snaps together, so be careful prying the tabs up as they are brittle. This sure worked for my '02.

Easy thing to do, $0 cost...worth a try at least.

 

That is NOT always the case.

My 99 had blinking 4HI/4Auto and 4LO. I found a broken vacuum line off the Actuator valve (on the firewall like described above).

I replaced the broken vacuum line and the lights STOPPED blinking and my 4WD now works great! Nothing electrical was touched.

The TCCM must have a way off reading low (or no) pressure readings. Probably not getting any readings from the actuator switch valve since their was no vacuum getting to it to activate it.

 

Maybe I misinterpreted the OP's problem. Sounded to me like they totally go off, then back on, which would indicate an electrical problem.

On the Auto 4 button, when they blink, it's telling you a trouble code is present in the TCCM, and in your case, the axle engagement switch was not being satisfied due to a lack of vacuum to the actuator.