First crazy snow storm of the year and I'm pretty sure my 4WD is not engaging. Last weekend was an ice storm and I didn't think it was working during that storm too, but figured it was just too icy. I had a friend with me today and he looked at the tires to see if they were spinning and he said no. The vehicle didn't feel like it was driving in 4x4. I also didn't feel the familiar vibration through the floorboards. On the plus side, I'm pretty sure I have limited slip differentials and I have snow tires.

Now back to the problem. It's push button, electronic 4WD. The green light goes on and stays on for 4HI. I am also able to engage 4LO and can feel it drop to a lower gear ratio, but I don't think the front wheels are engaging at any time.

I've had some issues with getting out of 4HI in the past, but that was when it was really cold. I meant to check and top up the transfer case fluid this summer, but don't I know of any leaks.

The vehicle is a 1994 S10 Chevrolet Blazer 4x4 W-Engine Code. I'm not sure which transfer case it is, but I saw the label this summer and it's a New Process.

Any suggestions, ideas, etc. are welcome. I've done some searching on the site, but it seems that the green light only stays on if you're able to engage 4WD? I'm also wondering if it's a bad idea to keep trying to use 4WD?

My first guess was the Transfer Case, but I am also thinking the front hubs???

 

After a bit of research I'm starting to think it's the vaccum controlled engagement system. But is it normal for the indicator lights to stay on, even if the 4WD is not engaging?

 

i would say check you vacume lines, i have the same problem on mine right now it will say its in 4wd, i can hear/feel the noise it usually makes but not in 4wd. i am going to check all my lines and i would say that is a great place to start

 

You have the single switch with 4hi and 4low, when you push the 4 hi, do you hear the actuator motor on the transfer case engage? If it appears to work then you need to check under the battery and see if the plunger is pulling the engagement cable. start there and let us know the results.

 

Okay, I got my vehicle out of the snow drift this morning! LOL! It still fells like there is no 4WD!

After I got out of the snow drift, I played with the 4LO switch and could hear the electronic actuator motor in the transfer case doing it's thing. So I guess the next step is to check the vacuum controlled engagement system. I am assuming that this is what engage the front wheels?

I have a Chilton and Hayne's manual and I can't find any information about how the 4WD system operates. Beyond the fact that there is a transfer case, a front drive shaft/axle/differential etc., but it doesn't get into details about how the 4WD actually operates.

I found this product which seems to explain the details, but I'm still not 100% on everything.

http://www.4x4posi-lok.ca/pdfs/troubleshootguide.pdf

I also found this:

http://autorepair.about.com/library/a/1/bl378.htm

and this:

http://wiki.answers.com/Q/How_to_cha...drive_actuator

So I think it's most likely the system that engages/disengages the front axle is malfunctioning.

 

Ok lets start up top first, disconnect the battery and remove the battery tray, under the tray you should see a round diaphramed plunger with a cable running to it. grab the cable between the bracket and plunger and try pulling the cable twords the plunger. if it moves freely youre good so far.
Try hooking up the battery without reassembling everything, start the truck, and engage your 4 hi or 4 low, Now did the plunger pull the cable? Page 8-15 of Haynes manual,clutch and drivetrain section.(plunger sucks in and pulls the cable back about an inch or two) If it didnt, then your vacuum switch underneath needs to be replaced, crawl under it and find the 3 vacuum line bundle and follow it to the vacuum actuator.

If all that checked out good and seem to be operating the way they should, then your in for a treat, tearing into the shaft.

Let us know the result of these things.....

 

I located the vacuum operated 4WD actuator, but have not tested it out yet. The weather is too nasty to work out there! I don't have a garage.

I will check all that our soon though First Gen... probably over Christmas Holidays.

I want to add something too though. I have been hearing an air leak in my dashboard for the last little while. I attributed the hissing sound to climate controls, but now I am thinking that it may be a system vacuum leak? I never thought much about it until the 4WD problems. The noise was bothering me but I never gave it much thought.

The hissing noise goes away when I accelerate. I assume that when I accelerate the hissing goes away, because there is suction somewhere else? Or am I totally off base and this noise is totally totally unrelated? My climate control fan is also fairly weak these days. I was going to replace it over Christmas holidays, if the nice weather continued to hold out... lol!

Yeah, I know, I've been letting things slide... but I've been super busy with school since the fall!

Thanks for everyone's help so far! I'll get back on this problem when it's a bit nicer and I have time over holidays. Until then, it's a good thing that I have good winter tires and limited slip differential on the rear axle (I'm pretty sure it's got LSD on the rear?)! But I really want my 4WD!

I'm adding another link here for my own reference and others. I don't have time to fix this now, but this post is very informative:

http://forums.s-series.org/viewtopic.php?t=50947

A picture of the Vacuum Actuator located under the battery:

http://www.monsterautoparts.com/CHEV...es/1430001.jpg


A picture of the 3 hose switch, located on the Transfer Case:

http://www.monsterautoparts.com/CHEV...4%20Switch.jpg

Correct me if I am wrong, but I believe it is a very simple pneumatic switch using a spring loaded ball to close the port and vacuum pressure to open the port to all 3 hoses. The vacuum switch is air pressure activated by the internal mechanical action of the transfer case entering 4WD. A verification of this would be appreciated.

 

Vato, I am having a similar problem and found that the website you mentioned (http://forums.s-series.org/viewtopic.php?t=50947) was very helpful.

Here's my problem if anyone can help: I can get my Blazer to engage in 4lo but not 4hi. When I press the 4hi button nothing happens. When I am in neutral and press 4hi both 4lo and 4hi buttons flash 5 times. Sometimes both buttons will stay lit and other times both will turn off. I replaced the vacuum actuator (under the battery) and still have the problem. I know I am getting a vacuum because when 4lo is engaged the actuator is compressed (I originally thought the problem was a lack of vacuum). After reading the website you posted above, I am now thinking the problem is with the encoder.

Quote from linked website "Encoder failure: Transfer case will not enter 4HI, but will enter 4LO. This is because the computer doesn't know exactly what position the case is in, so it just moves to either extreme (2HI or 4LO). "

Does this mean I need to replace the encoder? Or is there a problem with my transfer case?

Thanks for any advice
Chris

 

That is a good link. And since they copied it from somewhere else, I'll copy it into the 4x4 No Worky.... Maybe this will help.... thread, keeping the sources of course!!

As far as your issue candersonosu, it does sound like an encoder fault, but to be sure, you should check for codes. Checking for codes could be a simple DIY, or it could require a GM Tech2 (or equivalent full feature scan tool to access the TCCM). It all depends on what you are driving and what transfer case you have.

The three pronged switch on the transfer case is a mechanical vacuum valve. When in 2HI, the switch connects the vent line to the actuator line. This is its default position. When in 4HI or 4LO, the switch is activated and blocks off the vent line, connecting the actuator line to the engine vacuum line putting engine manifold vacuum to the actuator, drawing it in, and engaging the front axle.

 

So I just got done getting the error codes. I used that same website and used the second section titled "For OBD-II vehicles with push button between the instrument panel and the radio/HVAC control stack:". After grounding pin 13 and turning the ignition to run, the 4x4 lights flashed 2 times paused and then flashed 3 times. As stated these codes return a faulty encoder.

Would you recommend getting a diagnostics from the dealer? Or have I narrowed the problem down enough to the encoder? Also, do you think a used encoder from a junk yard would be worth the money? I looked it up online and they run about $165.!.!.. I am a poor college student!