Greetings all,

My vehicle is a 1999 Chevy Blazer LE 4.3L V6 with the 4 button 4wd control on the dash.

A couple years ago, I tried to engage 4lo while off road and after trying the dumb 4wd lo button a couple times, it finally engaged. Then it took a few tries to have the vehicle return to 2wd hi. After that, I could not engage 4wd hi or lo. (It may go into lo but I forget)

I took the vehicle to a shop and they diagnosed the problem as a bad encoder motor. I purchased a new encoder motor from Autozone, installed it, and still had problems. This time the 4wd lo would engage but would then not ever return to 2wd hi. I went to the GM dealership and they diagnosed the vehicle with needing a new encoder motor and they were able to get the vehicle back to 2wd hi. (it is no fun driving around town in 4wd lo). I went to NAPA and tried two different encoder motors, one I installed, and the last I had the dealership install. (GM wanted $$$ to buy their part)

I checked for corrosion in the TCCM in the passenger side kick panel and found no problems.

The 4wd still does not work and never has since a couple years back when I dealt with all the encoder motor issues. I keep the vehicle in 2wd hi and leave it there to avoid being stuck in 4lo sometime. There is a service engine light that comes on intermittently and sometimes the 4wd light comes on.

Any suggestions on possible fixes? I think any dollars I spend at a shop will have them tell me I have a bad encoder motor which I doubt will not fix anything.

I read earlier today about someone pulling off the encoder motor and manually shifting from 2wd to 4wd with a wrench multiple times to loosen up the shifter and that fixed their problem. Anyone ever try that with success?

Winter is coming and I really miss my 4wd....

 

Test the wiring. Actually ohm out each wire that runs between the switch, tccm, encoder motor, and all of the speed sensors. The wiring diagrams should be available in the Tech Article (DIY) section.

 

A friend of mine has a scan tool that might could help some. When I get a chance I'll test the wiring per the DIY article. Thanks for the reply.

 

Update 1 ....... Last night we hooked a scan tool (autoengenuity) to my Blazer but it only had the Ford package for additional tools and not the GM package. We pulled two codes off, P0171 and P0174 stating the system was too lean (Bank1 and Bank2) Those were the only codes we could get and nothing from the TCCM.

I tried to engage 4lo and 4hi while the vehicle was running and in neutral. When I tried that, the interior lights would dim but no engagement sound occured. I figured based upon the dimming lights that perhaps the shifting motor was trying to work but was meeting to great of resistance.

Today I dropped the front driveshaft, removed the encoder motor, and used a wrench to rotate manually the shifter protruding from the transfer case that the electronic shifter normally would rotate. It seemed a bit stiff perhaps but not too sure, and perhaps it loosened up a bit.

I then hooked up all the electrical connections to the electronic encoder motor with it not bolted into place, leaving the shifting location visible. A friend had the engine running and while in neutral, shifted from 2hi to 4hi and 4lo. While doing that, I could see the shifter on the encoder motor rotating.

I reattached the encoder motor and drive shaft, then tried shifting into the various drive modes.

It shifted into 4 Lo and most certainly engaged based upon shifting click and feel of torque. However the light indicator on 4 Lo would continue to blink and never would turn solid. The light on 4 Lo would turn solid for a brief moment when I would select 2 Hi.

I had zero problems going from any other drive range into 2 Hi. No sticking, very prompt, and light would turn solid.

4 Hi is very puzzling to me. When turning the vehicle on, it was the only light to not come on at all. When pressing the 4 Hi button, usually it would not light up any but sometimes it would flash a bit then stop flashing and never once turn solid. I did not hear an obvious engagement of the encoder motor when that mode was selected but there was some type of softer noise I could hear.

Auto 4wd would do basically the same thing as 4 Hi except the light would blink when pressed and would turn on briefly when the vehicle was started.

The vacuum system appeared to be in good order and the fact that 4 lo was obviously engaging leads me to rule that system out as a problem. There was a section of tubing attached to the vacuum system on the driver's edge of the vehicle just under the hood that was about 8" long and not attached to anything at the other end. Not sure what to make of that.

4 Hi and Auto 4wd may be truly engaged when I select them but I cannot be sure as I don't have jack stands.

I wish I could figure out the indicator lights and know for sure if 4 Hi truly engages or not. I've not done much of any electrical diagnostic work on a vehicle and despite some good charts and diagrams, feel a bit lost on how to start. I do have a multi-meter tool to work with.

At least I now know I can use 4 Lo and it will shift back to 2 Hi. The only real thing I did to the vehicle was manually shift the transfer case some. what a puzzle. Sure wish it was a manual.