Abusing of you guys, one more aspect: the code reader, will it erase the malfunctioning? If I put all the tires exactly equal before the erasing, does it mean the problem will be solved? (in the case the old tires are the origin of the problem).
I have the idea to use the code reader after buying the other two tires (some $160 each) but ensuring the fix. If not the rears are still good for some kilometres.

 

Lets move on to other diagnostics steps as I think we are all in consensus that the tire diameter difference is not enough to cause the issue.

The typical code reader cannot access the TCCM so you really need to do your homework prior to purchasing one. Reading the code is the major benefit of a code reader. Any code will clear it self after repairs have been made, but knowing the code will point you in the right direction for repairing the actual problem. Just clearing the code really does not give you much... You can clear the codes by disconnecting the battery for 10-15 minutes.

You can test the switch and do other general checks using the information in my post above. Please do have a read through them and do not just dismiss them. If you have any specific questions, please let us know and we will try to help it better detail.

 

In this moment the Blazer has 4 auto and 2 hi (at least in the cluster lights information). I understand that when 4 auto is available it means that the front diff is connected. That means the vacuum system under the battery (and the valve, hoses related) is OK. How can I be sure the front diff is locked when in 4 auto? ( I mean with the resources I have in my apartment and paved streets around everywhere). Frankly I do not feel any steering difference or sound due to front tires slipping during a sharp turn.

 

Finally I went to the main Chevrolet representative. They only got the general code of misfunction (C0387). And I paid $70 for knowing what I knew since day one. To advance in details they want another $100. The problem is that don't believe them and the result is doubtful and trial and error like.
The last minute pre failure (driving hard surface in 4 Auto) I felt the front wheels as dragging, like in the old conventional systems. Then the light of service come on. Is there any sensor for the level of lubricant in the transfer case?. I'm starting to think that if the front wheels dragged maybe the transfer case is below the level (tiny clutches did not work) and a signal was trigged. But most of all I'm starting to thing in my Blazer as a future 2WD.

 

Start with this:
C0387 - Unable to complete shift

If you cannot walk through the diagnosis, you are at the whim of a repair shop.

How do you mean that the front wheels are dragging?

As an aside, when in Auto4wd, the front axle will only be engaged when there is slip detected by the PCM. You can verify this by disconnecting the vacuum line which runs from your vacuum solenoid on the firewall down to the vacuum actuator under the battery. If you have vacuum at this location all of the time, then there is something wrong with either the solenoid, wiring, and/or the TCCM. If the solenoid is getting power all of the time, then there is something wrong with either the wiring or the TCCM itself. I do not believe that this is the cause of your C0387 code though.

 

Sorry, but after some readings I have to friendly disagree with you about the front wheels engaging only partial time. When the 4 auto is selected the front wheels are engaged all the time. But are not receiving power all the time. Power to the front wheels is sent only when the clutches are commanded (rear wheels slipping). I have the idea that my clutches are always sending some power to the front or at least they do not fully release (open) at the right time (so here is the idea of the low level at the transfer case, not yet reviewed).
Here is best explained: http://www.rsgear.com/articles/2004_12.pdf
In this article the importance of the very similar size of the tires is pointed. Thus I'm coming back to my first idea of the tires being the culprit. But I'm cheap.

*Combining Consecutive Posts*

In this report, the importance of the tire sizes is defined in 1/16:
http://www.transmissiondigest.com/te...09UpToStds.htm
I'm convinced that the new tires generated the problem , specially as I drove on a hard dry surface. Will all new tires fix the problem?. I need to send some $300 to get the answer. The rears are old anyway.

*EDIT by swartlkk* - Please use the EDIT feature to include more information in a previous post if another member has yet to reply. Consecutive Posting is prohibited by the rules of the forum.

 

In this report, the importance of the tire sizes is defined in 1/16:
http://www.transmissiondigest.com/te...09UpToStds.htm
I'm convinced that the new tires generated the problem , specially as I drove on a hard dry surface. Will all new tires fix the problem?. I need to send some $300 to get the answer. The rears are old anyway.

 

yes, you are correct, my mistake. Things have just been crazy lately.

If you are not willing to properly diagnose the problem, by all means, toss tires at it.

Will it complete a shift with all 4 wheels off the ground?

 

Tomorrow I'll do a try lifting and that.
The blue liquid is next as is easy and cheap to check. In the main Chevy dealer at least they have some pints.
later the tires.

 

Well, after a complete follow up at the main dealership (representative) and $300 later, they told me the transfer case actuator is fried. They want some $1100 for the repair, including the part. This is excessive for a $5000 vehicle. So I will try to import the actuator from USA. I need to ensure the part number. My Blazer is with 4 buttoms type transfer case, RPO NP8, model year 2000. Any of you have the GM part numberfor the actuator?, is the actuator the encoder motor?. There are encoders in EBay at $200 but not GM (or related) parts, any opinion?. Thanks for your collaboration.