last spring was having some tranny issues ( turned out to be valve body)
anyway.. i pulled blazer into garage and up on the ramps, had it in 4lo(easier to get up on ramps)well it has set there in 4lo on the ramps or jack stands (needed ramps for another project so jacked it up and put it on jack stands and removed the ramps)finally got everything i needed to replace valve body (purchased a used one), so i replaced valve body, put in new filter, put in new fluid, started her up, i'm in 4lo, no matter what i push(i am in neutral) 2hi, auto4,4hi, it will blink then go back to 4lo, i also hear clicking underneath drivers side, the t-case i think. i can pull forward, but i can't go reverse, when i shift to reverse i feel it shift, but no go, if i put it neutral and try to push out of garage, it doesn't want to go. i think leaving it in 4lo for so long may have something to do with prob. have read some other threads on subject, going to check t-case fluid tommrow. any ideas ,,or words of wisdom greatly appreciated.

thanks

99 blazer 4.3 4x4 automatic

Sounds like the dront diff isn't disengauging... Have you gotten it off the ramps? If not you may have to jack it up and then pull the ramps out then lower it. Sounds like simple pressure is keeping in place. Another option is to disconnect the battery for about a 1/2 hour and see if that helps reset the 4wd...

yes, its off the ramps, and battery was disconnected (neg cable)the whole time until, all put back together. after all back together started right up, put in gear to check my work,,felt it shift to all gears will go forward in drive or 3,2,1, and when i put it in rev i can fell it engage, but it will not go ..if i put it neutral get out and try to push it backwards still no go.. thanks

If you want to see if the Tcase has any error codes on it do the following:

-key off, connect pin 13 of OBD to a good ground
-key on, watch the shift buttons flash

No code: 1 flash and then off
One code: 1 or more flashes, 3 second delay, repeat
Multiple codes: 1 or more flashes (code 1), 3 second delay, 1 or more flahes (code 2), 3 sec.....

Report any codes back here and MT2500 should be able to let you know what's going on.

I still haven't properly fixed mine btw. I was able to get it back in to 2hi so I'm guessing it's the encoder motor (also known as the transfer case control module I believe).

If you want to see if the Tcase has any error codes on it do the following:

-key off, connect pin 13 of OBD to a good ground
-key on, watch the shift buttons flash

No code: 1 flash and then off
One code: 1 or more flashes, 3 second delay, repeat
Multiple codes: 1 or more flashes (code 1), 3 second delay, 1 or more flahes (code 2), 3 sec.....

Report any codes back here and MT2500 should be able to let you know what's going on.

I still haven't properly fixed mine btw. I was able to get it back in to 2hi so I'm guessing it's the encoder motor (also known as the transfer case control module I believe).

That won't work on a 99, only 94 and below ODBI systems, he has ODBII

That won't work on a 99, only 94 and below ODBI systems, he has ODBII

Correct me if I'm wrong, but there are only 9 pins on an OBD1 system, and 16 on OBD2. Given that this is done with pin 13 that pretty much makes it impossible to do on OBD1.

I did this on my 95 on Saturday btw...

tried to do this, took a wire and stripped back about an 1" on both ends, twisted up nicely and put in pin 13 took aligator cliped wire cliped on to wire in and clipped other end to frame interior with key off, turned key on all lights come on, then off then 4lo then auto4w blinks for about 30 seconds then goes out, leaving 4lo on.

You'll need to count the number of blinks between pauses.

Edit: Here are some better instructions I pulled from the s-series forum

1. Position the ignition switch to OFF. Ensure the ignition switch is positioned to OFF for at least 6 seconds.

2. Connect pin 13 on the data link cable to a vehicle ground source. The data link connector is located in the cab under the instrument panel on the drivers side.

3. Position the ignition switch to RUN.
Note the shift select buttons for blinking codes. Refer to Diagnostic Trouble Codes .

If the shift select buttons all blink one time and stop, and do not continue to blink, no fault codes are stored in the TCCM.
The transfer case shift select buttons will blink in order to identify any stored DTC. If only one code is stored in the TCCM memory, that code will blink repeatedly with a three second delay between blinking sequences. If more than one code is stored, the first code will blink once, then after a three seconds delay, the next code will blink. This sequence will continue until pin 13 is no longer grounded.

When reading the diagnostic trouble codes, the number of shift select buttons blinks will indicate the code number.
---------------------------------------------------
Diagnostic Trouble Code (DTC) 1
When the ignition switch is positioned to RUN the TCCM test to determine if RAM standby Power (maintained battery power) to the TCCM was lost since the ignition was last turned OFF. When power is interrupted on pin C6 of the TCCM, the TCCM stores a loss of RAM standby power.

Diagnostic Trouble Code (DTC) 2
During electronic shifting, the TCCM check the motor/encoder for normal operation. If the motor/encoder does not function correctly enough times, the TCCM stores a motor/encoder failure DTC 2.

Diagnostic Trouble Code (DTC) 3
The TCCM performs a test each time the electronic-shift motor is turned ON or OFF. If the motor does not function properly the TCCM stores a motor circuit failure DTC 3, and the shift select buttons blink in order to inform the driver of a problem.

Diagnostic Trouble Code (DTC) 4
Each time the ignition is turned ON, the TCCM tests the memory, the program, and the internal system in order to ensure that the TCCM is operating properly. If the TCCM detects a fault within the TCCM, the TCCM stores a RAM/ROM memory failure (DTC) 4.

When the TCCM is running a diagnostic, and a code 4 is displayed by the shift select buttons, replace the TCCM.