I bought a 2000 Blazer in Oct of '08. The transmission was replaced in July of '07 @ 103,000. The Blazer has 121,000 miles on it now. This Blazer has the Electronic Transfer Case, not the Automatic Transfer Case.
It snowed here this morning (first time this year :smile: ). My wife tried to put the Blazer in 4-HI and it would not go :frown: . The vehicle works fine in 2-HI.
When my wife arrived home this evening, I checked a couple of things out:
1.) The Blazer will go from 2-HI to 4-LO.
2.) It will go from 4-LO to 2-HI.
3.) If I try to go from 4-LO to 4-HI, it will go to 2-HI.
4.) If I put the tranny into Neutral while I am in 2-HI and push the 4-HI button; the indicator lights will flash, the actuator energizes, and it stays in 2-HI.
5.) If I am in any gear other than Neutral, nothing happens when I push either the 4-LO or the 4-HI button.
I wold like to know what may be keeping the vehicle from going into 4-HI. Thanks for any help!

Proper testing will answer many problems.

Pull codes.
Ground pin 13 on diagnostic connector turn on key and watch shift button lights for code/codes.
Post back the flashes on lights.

Also clear codes and see what comes back.
And tell us how the shift button lights do on key on bulb check and what they do when you try to shift it.

Have you checked all wiring and power feeds and fuse power and fluid level?

Hey Rider,

This may sound stupid but I have seen this work 3 times for this vintage Blazer when the TCCM (Transfer case control module) is quirky. Disconnect the battery for 5 -10 minutes and then reconnect it.

My 2002 Blazer would not shift at all and had been that way since last winter. Then my brother in law told me his '02 Blazer had the exact same problem last winter and the mechanic at his gas station disconnect and reconnected the battery and the problem was fixed. I did it last week end and it worked for me too. When I was talking about it to my brother in law my niece said her '02 Blazer was doing the exact same thing but it was stuck in 4 wheel drive (since last winter, can you say 10 MPG @ $4 a gallon, she's not to bright). After I fixed mine I went over to her place and fixed hers too ( I was amazed it worked again).

I think there is something flaky with this vintage TCCM because if you contact the dealer they will tell you the part number for the TCCM in your truck has been superceeded by a new part number.

Don't know if this will fix your problem because all 3 of the Blazers that I know about would not shift at all (two wouldn't shift out of 2 Hi, 1 wouldn't shift out of 4 Hi) and they were all '02 Blazers.

Give it a try, it doesn't cost anything.

Good luck,
Sparky

O.K. Here's what I have:

I have not checked out the codes yet. Will try to do that tomorrow.

Here is what the lights are doing:
1.) During start-up, all indicator lights come on for about 1 second. After that the 2-HI light stays on.
2.) When I shift from 2-HI to 4-LO, the 4-HI and 4-LO lights flash 3 times. After that, the 4-LO light stays on and I am in 4-LO.
3.) When I shift from 4-LO to 2-HI, the 4-HI and 4-LO lights flash 3 times. After that, the 2-LO light stays on and I am in 2-HI.
4.) When I am in Neutral and try to shift from 2-HI to 4-HI, the 4-HI and 4-LO lights flash three times and the 2-HI light comes back on.
5.) When I am in 4-LO and try to shift to 4-HI, the 4-HI and 4-LO lights flash 3 times. After that, the 2-HI light stays on and I am in 2-HI.

I just tried to drive the Blazer for a short while in 4-LO. It doesn't seem "right". I "feel" resistance until I am at about 5MPH, after that, it feels normal (like I am in 2-HI). (I HAVE NOT exceeded 15MPH in 4-LO!) I will check ALL electrical and vacuum lines I can find on this system.
Also, I read that there is a diaphragm under the battery pan that is used to engage the 4WD system on this vehicle. I will check for that tomorrow. I also plan to find the wiring diagram, pull the switch and ohm out the connections on the switch.
I will keep you up to date on what I find.
I appreciate your help in this matter.

You are welcome.
Try to get codes and post them back.
They only put out 4 codes.
1-2-3-4


The all data or a factory manual has the repair flow charts fo different code.
Also the wiring and switch and other test.

The front axel actuater is only for locking the front axel in and out.
The transfer cas has to shift right first and then the right front axel locks in.
http://www.alldata.com/products/diy/index.html

Let us know how it goes.
Good Luck

Thanks for the codes. I appreciate the info.

Here is what happened today: I removed the battery so I could check the condition of the diaphragm. The diaphragm seems to be in good shape. I also checked the connection of all vacuum lines and electrical wiring on the system. I did see some age-related decay on some of the vacuum lines. (These lines were in the driver's side area under the hood near the ABS and Cruise Control units.) I wrapped them in electircal tape since they were far away from any heat.
After I reinstalled the battery, I started the Blazer. Just for kicks, I pushed the 4-HI button. The indicator lights blinked once or twice and engaged! The Blazer went into 4-HI! I put the transmission into Neutral and engaged 4-LO. It also engaged. I put the Blazer back in 2-HI and went for a drive. I was able to get the Blazer into and out of 4-HI with no problem.
I am not sure if removing the battery did the trick to reset the TCCM or not. I do not think the decay on the vacuum lines was the culprit. I bought this vehicle from my sister. When I gathered information from her, she did state that the TCCM had to be reset one other time. Here is my next question; Should I replace the TCCM or let it go? If I do need to replace it, how soon should I do it?
Thanks for all your help! :smile:

Any codes?

Proper testing makes proper repairs.

If vacuum lines are bad replace them.
Vacuum lines is for front Axel lockup.

Transfer case shift is electrical.

I will try to have codes read this week. I'll keep you posted. I will check into vacuum line replacement as well.
Thanks for you help!

Hey Rider,

Told you reseting the TCCM was the easiest fix to try, didn't cost a dime and it didn't take too long.

If the TCCM is working ok now reading the codes will probably be a waste of time. When you disconnected the battery any codes that were set would have been erased. If and when the TCCM acts up again would be the time to check the codes.

As far as replacing the TCCM it is up to you, it is kind of pricey (hundreds of dollars) but I think that this issue is going to happen once in a while because there is a problem with the design of the TCCM. If you decide to replace it make sure that you get the new part number or this issue will just come back again.

Sparky