I have service 4x4 lit and no 4 wheel drive . The 2 hi light is on solid . If i push 4 hi or 4 low they blink then it goes back to 2 hi. I've been reading up and dont want to waste anyones time here but I ran into a problem while trouble shooting .. The switch has been re-soldered it had some cracked joints. The tccm has been removed cleaned and corrosion removed now it clicks when i push the buttons ...now the problem .. After pulling the battery/tray and restarting truck to check the acuator ..as soon as it pulls in with the battery out of the truck the truck stalls... any ideas ? Also with the battery back in and pushing 4hi / lo a buzzing sound coming from encoder motor ( which I think is the 4 wheel drive problem) but why the stall without battery ?? Ive seen others do it with no problems .. bad ground ?

 

Because you are exceeding the output of the alternator when the 4WD tries to engage. Looks like you may have a bad encoder motor and/or TCCM - hence excessive current draw and the alternator can't handle the draw at idle. Hopefully the transfer case is not stuck and immobile. Remember that bad encoder motor can also take out the TCCM electronics (it did on mine).

Check to make sure the transfer case is not stuck by removing the encoder and clicking through the selections using a wrench on the shaft. If not stuck, then replace encoder motor. If still won't work replace TCCM. From your description, it's not the controls.

ps Summit Racing can get you anything and will price match anything on the Internet. Plus 1-2 day shipping and no tax. They also have very liberal and easy return policies. So does Amazon. So shop around. Cardone parts worked fine for me.

But if you feel need to know for sure before replacing any parts, then a Tech 2 and a dealership is in order unless you go through the wiring schematics, understand the operation, and devise your own testing. Sometimes paying someone to do diagnostics cost more than all the parts possibilities when doing things yourself.

 

That makes sense .. The reason I asked on here was because I've seen it done and the engine doesn't die like mine did even with a bad encoder motor. I will pull the encoder this weekend and see if it cycles through .. I appreciate the response .

 

You should not try to make the encoder motor run when not installed on the vehicle. It can easily be damaged that way. It has a circuit that needs to be energized in order to release the brake on the encoder motor. Plus you will most likely have much difficulty getting it back on the transfer case if it is run to one of it's extremes and it moves fast - it's designed to only go back on with the TC in a certain gear selection. Furthermore I don't believe the internal position sensor works right if not installed on the shaft. Can't remember which position it needs to be in, but encoder instructions tell you and new encoder motors come with a plastic piece to ensure the correct position. How do I know?? I tried it with my brand new encoder motor and it really serves no purpose. Just because it runs off the vehicle does not mean it will turn the TC shaft.

Just take it off and make sure the TC can be clicked through it's range using a wrench. If the TC can and the TCCM clicks, then start by replacing the encoder motor as I described.

Now, if you want to disconnect the electrical connectors from the encoder motor (leaving it on the transfer case) and see if the engine still dies when you select 4WD, that could possibly tell you if the encoder motor is pulling too much current. But to me that already seems fairly obvious. Only thing I don't know is if the TCCM will also be junk from excessive current through it or from ineffective repairs (soldering on it).

good luck and best wishes for a successful repair.

 

The 4 wheel drive selection switch is what was soldered .. The joints were cracked and the lights would randomly go out and come back on .. I meant to use a wrench and see if the TC cycles not the encoder. I started with the in dash switch, TCCM, vacuum switch on the firewall, actuator now down to the bottom . I haven't changed the vacuum switch on the TC or the encoder so hopefully it's one or the other .. I'll let you know .

This caused my lights to randomly go on and off .. Not sure how this picture will upload but the 4 solder joints at the top in a row are all cracked all the way around. This is what was soldered .

 

Yeah I got it wrong. You did say switch was soldered and TCCM terms were cleaned.

If you want to check your switch operation with a digital multimeter, that can easily be done. Note that the indicator lights in the display are powered by voltage feeding back from the TCCM, so flickering lights there could also be from a TCCM or wiring or corrosion/connector problem.

https://blazerforum.com/forum/tech-a...rmation-41198/

FYI - vacuum switch is on the firewall for 4-button Auto 4WD. Vacuum switch is on the transfer case for 3-button 4WD. Not both places on any system. Hopefully save you some looking. Sounds like you have a 4-button NV236 if you have checked a vacuum switch on the firewall.

 

Yes 4 button .. Awesome thanks! I didn't know if I have the switch on the firewall that there is not one on the TC .

 

Ok ..what would make the actuator get pulled in ..almost all the way then it just releases like it lost all vacuum .. Vacuum switch? .. I squeeze the actuator in by hand with truck off and I hear a hiss.. I traced the sound back to the vacuum switch on the firewall . There is a tiny hole in the top of this thing that air comes out when I squeeze the actuator .. is it bad ?

 

I'm going to speculate. Don't know this for fact. But if it can't complete 4WD engagement in transfer case, I suppose TCCM will turn off the vacuum switch and release vacuum. Actuator needs vented with engine shut off so it will release 4WD and I suppose that pushing the actuator manually will push air through the vent if the switch is turned off.

 

Well then ... that at least shows me the switch, tccm, vacuum switch and actuator are all doing their part I suppose .. lol