I checked mine today and it appears that it is actually going into 4wd. A little snow helped the test. The light still blinks. This could be due to the shaft not being in the right position or the encoder not knowing it is? All in all I need an new encoder? Is there a way to test the encoder? resistance or apply voltage on a bench to check operation. What voltage should it get on the truck?

 

It looks like there are two people with similar problems in this thread. I've been following this since I've had ( and subsequently fixed my problem ) with 4wd.

One thing I noticed is both of you are still having blinking lights. If both of you have the Auto NP8 4WD, do either of you get the Service 4WD light on the dash? If you do, then you can read error codes from the Transfer Case Control Module that will help you in your diagnosis. Almost every part in this system is expensive and complicated, you don't want to guess too much. If you can afford that, then you can afford to have someone fix it for you.

The encoder is part of the shift motor assembly and is anywhere from $125 used to $230 reman and more new. The computer is that and more. You can't replace just the encoder.

It is difficult to bench test, but it is possible. You have to be VERY careful not to break it or you will buy a new one. The motor is only meant to go through a small rotation. Removed from the Tcase, there is nothing to stop the motor and the encoder can be wrecked. Sorry I am being a pain, but it is really easy to mess this up. Trust me.

If you can read the codes of the TCCM, maybe your scanner will allow you to read real-time data from the module ( a Tech II will ). It will tell you the states of each of the encoder channels - A, B, C and P. If not, get a schematic of the system and you can probe it with a volt meter. The encoder has 6 wires ( Ground, +8V reference from the TCCM, and four encoder outputs A,B,C,P ). The encoder outputs are hall effect switches and need the DC supply, plus they have to be pulled up by a resistor internal to the TCCM to +5V. If you mess that up you will FRY your encoder. Normally each encoder is either at about 5V or about 0V depending on what mode it is in. Each shift mode has a pattern of these channels on and off, it is not one channel per mode. I'm still trying to document my system, so I can't tell you which should be on or off for all modes. I know some of it, but I don't have enough time to dive too deep into it now.

Also, get the REAL gm service docs for your vehicle. The diagnosis of the error codes and the process to follow ( like Swartlkk posted part of back a while ago ) is very good.

Lastly, don't test your 4wd on dry pavement. That is not nice to the hardware, it is not meant for that. Sometimes, too, if you aren't moving when shifting modes, you need to roll a little to help it shift. If helps things to engage or disengage.

Good luck, hope this helps a little.

 

That is a big help.

The Service 4wd light is not and does not come on. I only see it when I first turn the key.

I will look for a scan tool. I think I need to start there and see where I end up.

I hear the TCCM clink when i change modes. I hear it change under the truck. I can feel it bind if I have traction while in 4hi or 4lo. I do not let it continue as I do not want to break anything.

When I shift to Auto4wd I do not hear anything happen. the light in the button blinks for a min or two and switches back to 2hi.

 

Whew! That was a long read Ok, It sounds to me like you are both having a problem with the TCCM not seeing the front axle fully engaged. So, either it's not getting the signal from the front axle position switch, or the front axle is not engaging. A very easy and quick check can help identify which scenario you have.
Raise the front wheels off of the ground.
Disconnect the Vacuum hose from the front axle control solenoid (the hose that goes down to the diaphram under the battery).
With a standard hand-powered vacuum pump, apply 20" hg vacuum to the front axle actuator vacuum supply hose.
Rotate the left front wheel by hand and check to see if the right one is rotating with it (it may clunk a little when you first turn it until the teeth align with the collar in the diff.).
If the wheels turn with each other, then the axle is locking together and you have eliminated alot of potential problems, at this point you should turn your key on and see if the 4wd indicator stopped blinking. after you run this test, repost with the results, and we'll get this thing fixed for ya.

 

I found my issue when working on the engine. The electrical connector on the front diff was loose. Plugged it in and it works great. Too bad I gotta replace the engine....[sm=headbang.gif]

 

What connector? is it the one that I posted on the first page???? If not please please please put a pick up!!!!!

 

It is under the skid plate on the front diff.

[IMG]local://upfiles/12798/5521C867C0D14873B728273DD80564BC.jpg[/IMG]

I think that is the one. It was not plugged in all the way.

I went out tonight and started it up to double check. It still works great.

 

Question about the black cone and the indicator switch.......is the switch supoosed to go in snug (like tightening down a bolt) or does it just keep spinning? I thing my black cone thing (don't know the real name for it) it stripped. I just put a new switch in and the thing just kept spinning and I thought it was normal, for some reason.