My car started to behave strange yesterday. The Auto 4WD light came on and it went in to 4WD. When I try to select 2HI it doesn't respond. The 4WD can be selected but it goes back to Auto 4WD almost instantly. 4LO seems to be unable to activate now, it has been working before.

When starting the car all lights in the selector goes on.
A few weeks ago I got the 4WD Service light go on a couple of days when starting the car, restart a few times and it went away. I had that problem a few months ago now and then and I did replace the switch and the problem went away until now. Could it be that the switch is bad?

I have read a few threads about this but can't really find one that suits my problem.

I haven't checked any vacuum hoses yet. Two years ago I did replace the hose going down to the actuator under the battery since it was leaking then.


Thanks

 

When the light blinks, the TCCM is saying that it is trying to shift to the selected position. If it never stops blinking and goes back to previous, then the desired position has not been reached. It is supposed to know the position by the encoder motor sensor.

4WD is very easy to diagnose if you have a proper scanner - but very difficult otherwise. If I had to guess without a scanner, I would first check all the fuses in the 4WD system and the two large (one red and one black) wires going into the TCCM for corrosion on the connectors. If that was OK, then I would then take the encoder motor off and make sure I could click through the positions manually. If that was OK then replace the encoder motor.

Note: Never try to run the encoder motor when not mounted on the transfer case. It will destroy it. It comes with a plastic piece holding it in the install position. You will have to match that position by turning the shaft on the transfer case.

Maybe this link will be of some use. Good luck! https://blazerforum.com/forum/2nd-ge...-blazer-89044/

ps. I'll be close to you in early September - a week of vacation in Copenhagen this year!

 

Thanks for the info.

After I wrote this post and reading some others I went out and checked the vacuum hoses and the main one form the intake manifold had sort of sucked itself flat. I did change that one a few years ago but apparently the hose wasn't good enough for this task.

I will change the hose tomorrow and hope for the best. When I drove it this morning it behaved normally until it got warm. The hose was probably OK until it got warmer. At least what I can hope for :-)

Well Copenhagen is at least closer than Indiana but still about 3000 miles from where I live.
It is a very nice town, if you're in the hold harbor you might find a building with my last name on it. It belonged to my ancestors. I'm infact 1/8 Danish :-D

 

Hmmm... Your profile has you in Stockholm, which is only 660km from Copenhagen. Are you not in Stockholm?
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Oh, sorry it got one zero to much. And I'm 120 km south of Stockholm.

 

Good luck and best wishes on your repair

 

Well a new vacuum hose didn't solve it. It behaves the same.
Like many who have had the same problem.

I can get it to run in 2HI but after a while it shifts over to Auto 4WD and after that sometimes to 4HI. After a few pushes on the 2HI button it will switch over to that mode.
The relay under the dash is working and I hear it clicking when I get it to switch over to the other mode.

Sometimes the 4LO start blinking but it never switch over to that mode. It can start blinking during driving or standing still in Park.

My code reader doesn't see the transbox on this car, it does on my Opel.

I checked your link above and saw the Scantool recommendation.But I'm not sure what to select since your post have a few years on it and stuff like this updates quickly.

Will the ODBLink MX+ work for me OBDLink MX+ Bluetooth OBD-II Scan Tool for iOS, Android, & Windows
And then the Scantool software: OBDLink SX USB OBD-II Scan Tool for Windows


If so I will order that so I can get the proper diagnose on this problem.


Thanks

 

Sorry but the software/hardware described in my old post from 2015 (Scan XL Pro and OBDLink SX) will not read the 4WD system on your Blazer more than fault codes and do a TCCM reset. The only scanner I am aware of that will read the TCCM is the Tech 2. There are some clones from China for several hundred dollars US. There is no good inexpensive solution. Reading the codes in itself did not help me any in my diagnosis. In the meantime, during the past 8 years I have been reading/advising 4WD problems here in this forum and have learned a lot.

I recommend doing what I outlined in post #2 unless you have access to a Tech 2 scanner or something that will read and control the TCCM and have access to the factory diagnostic procedures. If you read the operation of the system in the link that I sent you will see that the TCCM translates the position of the TC from the encoder motor and sends a voltage to light up the appropriate button on the controls. When you select a different 4WD function, the controls sends a different resistance to the TCCM and the TCCM 1) starts flashing the newly selected button on the controls 2) unlocks the encoder brake 3) sends current to move the encoder motor to the new position 4) newly selected button goes to solid illumination when new position has been reached and current to the encoder motor is stopped. Push button controls are super simple (never really go bad unless broken) and the TCCM makes all the decisions/sends all the current. Encoder motors have two functions. One function is to tell the TCCM what position the transfer case is in. The other is to take current from the TCCM and actually move the transfer case shaft.

Encoder motors are almost always the problem because they run on high current to make movement in the TC. However a bad encoder motor or bad connections to the encoder motor at the TCCM can ruin either or both since high current runs through both. So if you have to take an educated guess because proper diagnostic equipment is not available, you check the connector on the TCCM for corrosion (post 2) and if it still doesn't work try the encoder motor first - excessive current draw is usually the root cause of all problems. Back in 2015 I had to put both encoder motor and TCCM on mine - plus clean connector terminals. These modules aren't cheap. I used rebuilt modules from Cardone. Make you wonder if we have really progressed from a simple lever. But have had no problems since that time.

To me it sounds like your encoder is sending wrong position information back to the TCCM. I have heard it is possible to replace just that part of the encoder motor, but with high failure rate for entire encoder I think it is best to replace entire assembly. In any case, always check the TCCM connectors and turn the encoder shaft with a wrench first before replacing anything. The TCCM is behind the passenger kick panel (right side of foot) - simple and easy to get to.

 

Update, drove it a short bit this evening and from the start it was in Auto 4WD nd refused to change. Then after a few hundred feet it changed over to 2HI and stayed there for the trip, just about 5 minutes. Then when going back home it started in 2HI and after a short while the Service 4WD light went on and stayed there until I turned of the engine. It stayed in 2HI for a bit longer but went over to 4HI. Then it stayed there and I wasn't able to change it.

When backing in on our parking lot it was engaged in 4WD. We have a set of a bit wider tires with more back spacing and when 4WD is on it is really struggling to move when wheels are turned. Now in the summer it is really heavy, not so much trouble when icy or snowy in winter.

After parking and turning on the engine again the Service 4WD light was off.

Is the TCCM located behind the glove box on this model, 2002 Blazer?

 

It is in the kick panel to the right of the passenger's feet.