For months now the 4 wheel drive switch on my Blazer Zr2 has been acting very strangely. Here's the story, a few months back I noticed that the light signifying that I am in 4-wheel HI was lit when I knew that it indeed it had not been put in that. A minute later the light changed signifying that it was in the original 2-wheel drive setting. As time went on it proceeded to get worse especially when on the highway. The good news is that it is not in fact engaging anything when this happens and I am able to cleanly move in and out of 4 wheel drive when it thinks its in the correct setting and shows that its in 2 wheel drive but when it is showing 4 wheel HI it will click twice and won't move into 2 wheel drive i'm assuming it can't because it already is mechanically. So the only way for me to engage it into 4 wheel Hi when this happens is to move it into 4 wheel Lo and back to 4 wheel Hi because when I hit 4 wheel Hi it doesn't do anything thinking it is in that position. The scare is if I engage 4 wheel drive that way it opens me up to being stuck in 4 wheel Hi until it realizes what setting it is in. It's pretty hard to explain but it seems to have a mind of its own and leaves 4 wheel lo completely alone. Any help would be very appreciated since snowfall is right around the corner and id hate to have a mechanic rack up the labor costs trying to figure it out.


Iv tried unplugging the tccm and plugging it back in and disconnecting the battery but no dice and have read other problems like this but theirs actually engages mechanically by itself unlike mine. With it freaking out and switching so rapidly putting on a light show sometimes I suspect it might be a electrical issue and even the switch itself but I would like to poke around a bit for tips before i do the old pull and replace route haha

 

My suggestion is to reflow / resolder all the electrical connections in the switch assembly. Be amazed as to how many problems an intermittement connection can cause.

Just be sure to be careful when separating the two halves of the switch assembly so as not to break the plastic. And use a low wattage soldering iron...not a soldering gun.

Good luck.

 

So you say"4 wheel drive light on but no action!" remove the switch from the dash assembly.You`ll need a volts meter for the next step..If and when you press all the buttons,all of the buttons light up..You know your getting power to the switch.You`ll have to find out what wire or wires that leave the switch going to the next station.Not fimilar with how this system works,It `s just trial and error.Ex: Say you have a light that doesn`t work in your kitchen,check the bulb first.If the bulb or bulbs are good,light still doesn`t work?Go to the next step, want to get a multi meter set it on volts.You will want to make sure your getting power to the switch,If your getting power to the switch?Go to the next step.Disconnect the wires all together @ the light fixture.Test the wires coming from the switch to the light fixture.If your getting power..Go to the next step,turn the light switch off re connect the wires at the light fixture.Turn the switch on, test the light fixture itself.If your not getting power @ the light fixture..You have a bad light fixture.Same procedure on any electrical problem.Start at the source, move your way down to the last step.

 

There are a few tech articles with the related wiring diagrams and connector pinouts to assist you in your diagnosis and others in their lack of understanding on the subject; NV233 transfer case / encoding motor switch for the 3-button setup and NV236 Wiring & Diagnostic Information for the 4-button setup. When you get into testing things, you will want a multimeter capable of reading voltage, resistance, etc. A straight up volt meter will not do you any good in a powered down and/or disconnected system.

The switch in the 3-button setup has a wire from the switch to the TCCM for each button. This is more simplistic than the 4-button switch that uses only one return wire and resistance changes between button pushes at the switch to communicate with the TCCM. Since the 4-button switch uses resistance, it is highly susceptible to influence from corrosion.

I am guessing that you have the 3-button system though as you have not mentioned Auto-4wd in your post. But please verify and I can provide further guidance. This isn't as straight forward as a home lighting system though.

Let us know if you have any questions along the way.

 

Thanks for the help guys i'll start looking around for bad connections and test readouts when I get a chance tomorrow.

Today I started to mess around with shifting in and out of 4 wheel drive to get a better description of my problem after not messing with it for a while (weeks) and ended up in the "stuck in 4 wheel hi" situation but his time it seemed like it was attempting to get into 2 wheel drive giving 1 click followed by 2 rapid clicks when it will usually only gave 2 spaced clicks from the tccm. While stuck in 4 wheel Hi for the mean time, i switched from 4 wheel Lo and back to Hi cleanly testing it out and drove off to my destination hitting the 2 wheel button every so often until it would shift back into 2 wheel drive. Then all of a sudden without stopping fully or depressing the clutch fully one hell of a scare happened. It threw its self into 4 LO letting lose a grinding noise similar to when you are trying to shift into a gear without fully depressing the clutch loudly. I pull off the street to find that none of the other buttons were responding believing that my fate was sealed for a minute with face in palms. I gave it one last go and like a act of god slid right into 2 wheel drive and I drove off with no problems. I'm starting to believe it might be the TCCM at fault but ill figure that out tomorrow. BTW yes it is the 3-button switch.