Just as the title says, 2Hi works fine and I can easily get into (and out of) 4Lo. When I hit the 4Hi button, the switch lights flash but it won't shift into 4Hi and reverts to whatever it's in (2Hi or 4Lo). Tried shifting to 4Lo first but still no go. Dash switch was replaced about 3 years ago and I probably haven't been in 4wd (either Hi or Lo) a 1/2 dozen times since. Since I can get 4Lo, I'm thinking the encoder motor is probably good but I'm not a mechanic by any means.

Any assistance would be greatly appreciated. Not sure it's worth my money to take it to a shop for a high dollar fix as I'm rarely in 4wd. With the upcoming foot of snow we're supposed to get, I'd like 4Hi for obvious reasons.

Thanks to all!

 

I had this exact behavior in a 95 Blazer last year. It was the encoder motor at fault. I replaced the encoder motor, reset the ECM and 4HI has worked for 2 years since. By ECM reset I mean disconnected the battery for 15 minutes and reconnected it.

Don't fret too much about the snow, 4LO and a decent set of AT tires got me through months of snow and mud.

 

Thanks. I'll wait til spring and have someone else replace the encoder motor. From what I've read/seen, sometimes you have to remove the front driveshaft. Too big a project for me. 4Lo seems to get me where I need to go but it would be nice to go faster than 20 mph in this kind of weather.

 

I felt the same way about driving slow in 4lo when 4hi is desierable. Also felt the same way about removing that front drive shaft and maybe the yoke to install such a small part.

I'm not saying you should attempt it the wrong way either, but I was able to change mine without removing the drive shaft with some minor scratches and removing some plastic.

 

I don't care about some minor scratches, especially under the truck where nobody will ever see them. It's not a show truck, by any means. What "plastic" did you have to remove?

 

It was a huge pain, I really don't encourage this it. In my circumstance I had a few beers and felt like I could do anything.


Taking this sensor off the motor is unlikely to be supported by Dorman or the warranty. I didn't care because if it broke the motors functionality I was going to just buy a new one. I had this encoder motor on hand for a long time prior to replacing it.


I fought the old one off, which might be where the plastic needed to be broken off because I couldn't disassemble the encoder while it was on the truck.


On the replacement I removed some or all of the screws for the encoder electronic sensor portion marking where it was seated. This is held in place on the Dorman part # I bought with large head Philips head screws, enabling this next part. I installed the replacement and then retightened the parts for the sensor with pliers where I couldn't fit a screw driver or Philips bit thanks to the drive shaft.


Remember to reset the ECM, or the new one will act like the old one until you do because the tcase and ECM remembers all the error codes it encountered until the ECM reset (battery disconnect).


If you can get the old one off there is a strong chance you can get the new one on. There is almost no clearance between the shaft and the motor to get the motor over the shifter attachment on the tcase. By the way, I used a wrench to manually shift the motor to 4hi just to make sure there wasn't a mechanical issue that the encoder motor ran into during operation.

 

yeah, don't do that ↑.

Taking out the front DS is simple.
Remove 4 - 11mm(?) bolts from front u-joint straps. Pull u-joint out of yoke. Wrap u-joint in tape so caps don't fall off. Slide DS forward, up and to the side a bit, but don't remove it from under the truck. If it doesn't slide easily off the TC output shaft, just give it a whack with a rubber mallet or a 2x4 to free it up.
Now you have plenty of access to the shift motor.
Re-installation is the reverse of taking it out.

Edit: While you're under there, it's a good time to replace the TC vacuum switch and inspect/replace the vacuum lines. The vac switch is less than $20.

 

Thanks to the both of you. I'm not much of a drinker so the beer-steeled-me-to-do-it thing probably wouldn't work. Will the ECM always throw a code if the encoder motor is bad? The last time I checked (about 2 months ago...I've had a purge valve solenoid CEL for a couple of years), there wasn't a code for the e-motor. Hate to bother with it just to find out it's something simpler (and/or less expensive). My truck is decent but it's JUST a driver. Nothing for show and nothing off road. If I lived a bit farther south, I wouldn't have even bought a 4wd this time. That said, 4wd would be nice as the streets in/around my neighborhood don't get plowed well or much.

 

Something else you may checkout is the TCCM,Transfer Case Control Module,located under the passengerside kick cover,small metal box with alot of wires located right of your foot when seated,under cover. I had the very same problem with my 2000 Blazer 4X4! Replaced it and problem solved.