First let me say that I have searched and read most all the post on this topic and have tryed some things but need a little more specific help if possible.
first, 1999 blazer 4.3l 4x4 shift on the fly, NO auto 4wd.

4wd was work fine, then just this week as the weather turned bad so did the engagement of the 4wd.

This is what happen's, I push the 4hi button and it clicks from under the dash on the passengers side(as it should) the light comes on for a second on the 4hi button then instanly goes back out, all the time the 2hi button light stays on, then a few seconds later a loud CLUNK and the 2hi light goes out and the 4hi comes on. When I put the 2hi button again to disengage it works fine, no noise and it switchs to 2hi. I have tried this at different speeds, stop etc. The last time I pushed the button it didn't make the CLUNK noise it was grinding like the gears were trying to mesh but didn't, I stopped instantly and hit the 2hi button agian, no noise and back to 2wd with no problem.

I have check the vacume canister under the battery tray, appears to be fine with no holes in the rubber and the cable seam to be working. I check the 4x4 fuse in the panel on the end of the dash, no problem.

I would like to read the codes from the button lights but don't know whick pins I need to jumper. If someone know this let me know.
Any help would be great, I hope I have provided enough info, if not let me know what else you need to know.

Thanks
Scott

 

Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes
The lights should flash 1,2 3, or 4 times for code 1,2 3 or 4.

That's the starting point.

If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.


• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.

• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.

• This sequence will continue until PIN 13 on the DLC is no longer grounded.

 

Clunking could be normal if your engageing the t-case on dry surfaces.

 

check all vaccuum lines

 

Chevy Lover
Do I just count the pins from left to right starting at the top to find pin 13? also, are one of the pins ground? I found the diagram someone posted that
shows the plug but it doesn't have the same pin locations as the one I have. Only some holes have pins in them and they didn't match mine. I think it was an older model.
Thanks

Hanr3
All the test were done on snow packed roads, I live in Canada eh!!! and we just got the first storm this past week. I use the 4wd a far amount in the summer also so it is
not from lack of use, it just started doing this?

4lowlife
Vacume lines. Obviously there must be one going to that actuator under the battery, does that come from the Tcase? It may just be vacum, it acts like the tcase is engaging but
when the hub go to engage is when it make the noise, and vacume runs that actuator right? which engages the hubs? Is this correct? That's the only vacum line I know of, can you direct me to others I should check?

I will check the codes and the vacums as per your guys suggestions and post back.

Thanks

 

Hanr3, I just seen your post on the 4x4 no worky, this will help me alot. thanks

 

Yea, that should help with the vacuum lines.

 

i agree with 4lowlife, i had the same problem in my 99zr2, also my heat only came from the vents, i checked all vacuum lines, and ther was one with no plug in it, i plugged it, and now my 4wd and heat works fine.

 

I have just had time now to replace the vacum lines, busy over Xmas and didn't need the 4x4.
So yesterday I replace all the lines as per some good articles in the forum. Wasn't that bad of a job just
that I didn't find any with a visible leak. Try the shift again and stil no worky. This is what happens when I push the button for 4hi - the 4hi light comes on and the 2hi light stays on at the same time. I then hit the 2hi button again and then both the 4hi and 4lw lights flash once and go out, still in 2wh drive. After doing that twice now neather button for 4wd works. Have to reset by unhooking the battery, which I have done before. I have followed the instructions off one of the post that said if you push the 4hi button while in park and try to trun the transfer case shaft and it doesn't turn then it is vacum. that is my case but now that I have change all the vacum lines and still no work. I have checked all the fuses on side of dash and under the hood, all good.
A mechanic here at home said that it could be the switch on the dash no working right. Could this be the case? Also I haven't check to see if there are any codes because I don't have a reader and don't know which pin is 13 to jump to ground. If you count the pin holes in the DLC under the dash, position 13 is empty?

Any more suggestions would be appreciated.

thanks

 

OK, let me start by saying that ITHINK your problem is being caused by a faulty vacuum switch on top of the t-case. Or you could have a low vacuum supply from the engine (mechanical problem).
That being said here is what you are asking for...

here are the 2 most common failure code charts...actually they are the ONLY codes that I have ever experienced in any of these.


[hr]


DTC 002
Circuit Description
The transfer case encoder motor is an assembly which houses four separate channels. These channels are used to indicate to the transfer case shift control module the present gear position of the transfer case or if the transfer case is in transition between gears. The encoder motor assembly consists of an electronically conductive inner ground ring in contact with a three legged wiper arm. Each leg's length is such that it makes contact with the conductive regions of the four channels. When any leg of the wiper arm is making contact with the conductive area of any channel, the encoder provides a path to ground to the inner ground ring.
During electronic shifting, the transfer case shift control module monitors the transfer case encoder circuit for the proper operating sequence. If at any time during a shift, the encoder changes from one position to any position other than the next possible position, an error counter in the transfer case shift control module increments by four. After the counter reaches 32, the transfer case shift control module set a DTC 2, a permanent "encoder fault," and reverts to a 2HI to 4LO or a 4LO to 2HI shift pattern only. To guard against a transient, random encoder fault due to vibration, dirt, electrical noise, etc., the fault counter reduces by one each time the transfer case shift control module detects a valid encoder value. The encoder must intermittently fail 25 percent of the time for the transfer case shift control module to consider it faulty and store DTC 2.
Conditions for Clearing the DTC
The condition for setting the DTC is no longer present and a momentary loss of battery power at the battery positive voltage circuit (CKT40).
Test Description
The numbers below refer to the step numbers on the diagnostic table.
[ol]

This step measures the voltage between the transfer case encoder circuit channels P, A, B, and C to ground.

This step tests the suspect circuit(s) for an open, short to power, or short to ground.

This step tests the encoder signal ground circuit for an open or high resistance.[/ol]


DTC 2 -- Encoder Fault



Step

Action

Value(s)

Yes

No


1


Important
Check the transfer case shift control module for DTCs. The transfer case shift control module is not a class 2 device. DTCs are displayed on the transfer case shift control switch. Use the following four steps to obtain DTCs.
[ol]Turn OFF the ignition for 10seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. [/ol]

Did you perform A Diagnostic System Check - Transfer Case?

--

Go to Step2

Go to Diagnostic System Check


2

[ol]Disconnect the connector at the encoder motor.
Turn ON the ignition, with the engine OFF.
Measure the voltage between the transfer case encoder circuit channels P, A, B, and C to ground.