ive been going crazy trying to figure this thing out, i have been searching for 2 weeks now. i have replaced many parts and tested many things. now im stumped.

2000 blazer 4x4 3 button switch.

-all 3 lights on switch flash when i start the truck
-no lights stay lit indicating what mode the truck is in
-pushing any button on the 4x4 selector switch does NOTHING unless the transmission is in neutral.
-in neutral i can hear the TCCM clicking when i push 2hi,4hi, or 4lo.
-i can hear the encoder switching from high to low when i push the appropriate button (but only in neutral)
-when in neutral if i push 4low i can hear the transfer case go to low, but i can also crawl under the truck and spin the front driveshaft by hand.
-occasionaly it will actually go into 4 low and engage the front axle. if it does, i can then hit 4 hi and SOMETIMES it will go in to 4hi.
-in order to go back to 2wd, i have to shift the trans into neutral, otherwise the switch is still dead.
-the switch on the dash NEVER indicates any of this....sometimes it will light up 4hi and 4lo, but ONLY after i actually get it to lock in.
-diagnosis test gives me code 1 and 2.


so far i have....
-replaced TCCM
-replaced encoder
-removed every pin and cleaned TCCM harness (replaced pins as needed)
-check continuity between TCCM harness and 4x4 switch / encoder
-tested all powers and grounds with DMM at encoder,tccm,4x4 switch, and front axle
-replaced any bad vacuum lines
-replaced vacuum check valve.
-replaced neutral safety switch


so now im at a loss.....most confusing part is, why does it only let me push buttons in neutral?

thanks for the help
joe

 

thats the way it works... You cant shift into low range while driving . Some models let you shift into high range at low speeds only but thats about it.

Have you tried shifting into 4hi at a low speed? Please dont try this over 5 mph.... The truck needs to be cruising at a really low speed to shift into 4hi Or else any faster will break something...

I personally never shift on the run . I rather be at a dead stop while putting my 4x4 on.

Click on this Link It should have all the information you need 4x4 No Worky.... Maybe this will help....

 

Have you checked the Actuator under the battery. It engages the front axle.

 

i should be able to shift into 4hi at any speed.....i should also be able to shift into any selection from park.....MY SWITCH WONT DO ANYTHING unless im in neutral. the buttons wont illuminate, or the tccm wont click any internal relays

 

wouldnt i still be able to TRY and engege the 4x4 from park or neutral? as i said sometimes i can get it to engage.

 

Read that link I gave you... That should have all your answers.

 

been there read all that, as i said i have been doing research for weeks.

maybe you found something in there that i didnt see and already cover.

according to your link:

"There are 2 types of shifts - mode shifts, and range shifts. A mode shift would be from 2HI to 4HI, and vise versa. A range shift would be in and out of 4LO. You can Mode shift any time when moving, but must be stopped in neutral to do a range shift."

i cant "mode" shift unless im in neutral either.

now do you understand?

 

Just had to step in and say something here. That is not true, yes im sure it is better to switch at low speeds but i can be driving at 40-50 MPH and throw it in 4HI with no problems and i often do, sometimes i will hear a clunk from the front when it goes in but thats not a problem.. If things start to get bad and you need 4WD you shouldnt be going 40-50 anyways but NEVER stop. Or else you might not get going again.

To the OP, im dealing with this issue with my other blazer as well. I have kind of concluded that i have bad vacuum somewhere along the line. Have you checked the actuator under the battery tray to see if it moves at all? If thats not it my guess is the TCCM still, even tho you replaced it. Things can be bad out of the box, but before you go replace it again we need to figure that out for sure.

 

my vacuum is strong, i have NOT removed the battery to check the actuator simply because occasionaly when i get the buttons to "workish" (in neutral) i can somehow get the front to lock in when its goes into 4-low. so i know that the actuator CAN work. i feel its a mater of it not getting the comand the rest of the time. especially since i cant even command it to go into 4wd unless im in neutral. i cant see the actuator causing that.

as far as the tccm goes. i have swapped between 3 used modules. all 3 do the same thing. considering it is a very ODD 4wd issue, i felt it highly unlikely that all 3 tccms had the same crazy 1 in a million issue.


when your saying "i am dealing with this issue to" you mean you also cannot control your 4wd unless your in neutral? and then its flaky? or you just mean yours isnt working either?

 

Well yeah mine is flaky too. I can usually get it in just fine but getting it out is the problem. I have to do almost the exact same steps to get it out as you have to do to get it in. When im taking it out of 4WD i can push the buttons all i want and they wont do anything unless im in neutral like you. So not the exact same problem but close