4wd issues... 2000 blazer 4dr 4wd
 

Hey all I was looking on the forums and didn’t find any that seems like my issue. So I have a 2000 blazer 4dr 4wd where my 4hi does not work but my 4lo does (I think). I say I think because I definitely feel it clunk into 4wd and it definitely feels like there is more torque. I have the 3 buttons on the dash. When in neutral and rolling to get into 4lo the button will blink a few times and then it will clunk in. With 4hi whether I am parked, driving, in neutral or anything and press the button it will light up and stay lit (as if it worked) but will not engage into 4wd. I have had the vacuum lines changed, the transfer case is good. My most recent trip to the shop it seems that everything works and the shop says that the issue is in the front differential. You can hear the relay/module thing over by the glove box and the transfer case switch when trying to switch into both 4hi and 4lo. Like stated, the light switches on and stays lit for both, the only difference seems to be that the from diff engages with 4lo but not 4hi.

my question is. Has anyone else had this particular issue before? I don’t understand this, the shop says it’s the front diff but the Front diff engages fine in 4lo, which doesn’t make sense to me that it would be a diff issue if it works in one of the modes.

i also have a wub wub wub oscillating noise coming from the front passenger side, I’m not sure it has anything to do with the 4wd issue ( the shop says it does) although the noise just started a couple months ago and the 4wd has had the same issue since before I even bought it.

any thoughts and spitballing ideas would be fantastic, I just want get some thoughts before I shell out $800 to fix a issue that I’m not sure about

Check the actuator under the battery, might have a tear in it,

Hi there and welcome to the forum! The "wub wub wub" sound you describe sounds too me like your passenger side wheel bearing hub assembly needs replaced... I have a 98 4x4 and mine was making a humming, rubbing kinda sound until I replaced the hub assembly. The part cost me $110 bucks plus tax and the labor cost for me was a 12 pack of beer and grilling some burgers and chicken on the grill :) My son in law did the work for me, took him about an hour and a half... That really isn't bad since he didn't have any air tools...

I'd bet it's not actually going into 4low, but is just going into 2low. Have you tried a sharp turn (at slow speedispeed) while in "4 low?" The front should jump or feel a bit sluggish if the front axle is engaged. That is my best guess at narrowing it down.

I have never heard it put that way lol, 2 LO... I always thought it's 2HI, 4HI or 4LO on the 3 button switch. I have no knowledge about the 4 button setup though...

Am having the EXACT same issue on 2004 Blazer, and am finding it hard to figure this is any sort of "unique" issue. The TCCM is the most likely culprit (somewhat expensive when you compare the cost to the value of the vehicle) so I'm going to dig into what the options are - so far, not finding anything other than replace TCCM? - Most folks say you can remove it (apparently access is easy) to see if it's working, and then some are saying you can "clean it" and it might start working again? - either way, most common temporary solution is that you can disconnect battery for several minutes, this will then "reset" the code that is recognizing problem, and stops it's function. - My question is: why will it then work again? it's either broke, or it ain't right? sheesh.
Good luck to you, I'll chime back in if I learn anything worth repeating! - And to those of you who might know the fix, please advise!

I had this issue last year and the one thing that worked for me but I never saw anyone suggest is: Check your vacuum lines! If you're also having issues with your HVAC controls not putting the air out where you tell it to, it's a vacuum line. Mine was burned on the exhaust and after replacement, everything started working again like magic. I had the "4 LOW" clunk and gear reduction but no power was actually going to the front wheels. The LOW is separate from the 4WD since it's a physical gear reduction part of the transmission. Drove around in the freaking snow at a snails pace but still in an open diff 2wd reality! Check the simple stuff first before getting rust in your eyes checking actuators in the mud. ;)

Strangely enough, after disconnecting the battery for about a half hour, then reconnecting it - it seems to have solved (at least temporarily) the issue. I have a code reader, and it will be my next tool if the issue comes back, but this may be a drivetrain code I don't get with my tool? Much like the intermittent Airbag warning light. Driver side airbag sensor is most likely the culprit there.

The 4wd has been put through the paces several times since the "reset", so the issue here for me is "intermitttent" for sure. frustrating none the less. Will update if / when the actual repair is unavoidable.

hey everyone, first off thank you for all the replies. I figured I would post a quick update. I did wind up going to the shop to spend the 800 to fix the issues, I didn't want to deal with it myself and with winter coming I figured 4wd would be worth having. The shop I think screwed me a little bit, they wound up claiming it wasn't just a few parts and replaced the whole front diff (well they frankensteined mine and a used one from a scrap yard, which i found out AFTER) and then they wound up charging me double the quoted price. It sucked, but I paid it and thank god I had 4wd (I'm in the northeast where we just got hit with the big snow storm). The oscillating noise did NOT get fixed with the 4wd, as they promised it would, so I'm still stuck with that. it got slightly better when I got new tires and a alignment but did not go away. The shopped claimed that the diff was just completely toast. And since then I have also been having a issue with brakes, which I think I have narrowed down to the brake booster. Overall getting 4wd fixed was definitely worth it because 4lo paired with studded snow tires (cooper evolution winter) made me able to crawl through the 24 inches of snow I had in my driveway. My first winter with my blazer and I'm super impressed so far (although I might add some weight in the back for when I'm in 2wd.

also to respond to some of you:
-I had no codes being thrown for the 4wd, only code I had and still occasionally have is a evap code (whole entire evap system, fuel lines, gas cap, everything was replaced by last owner, I think my blazer is one of the many with the gas cap issue as when they replaced the gas cap it fixed it for like 6 months)
-I did check the vacuum lines and had them replaced, I think they were bad, as things were acting different after replacing them
-I am starting to think the one noise is a hub, although it is not a typical hum from a hub, I have a bunch of rusted out parts in the front anyway so I was planning to replace the hubs and a few other things while I'm at it. I usually have a dead Jan and Feb so I can work on it then.

Thanks for the update. Such posts are super helpful.

Regarding the vacuum lines, oftentimes the HVAC system acts all wonky due to vacuum leaks. Did you find that system working any better?