Two years ago, the 4WD switch buttons started acting up. It would light up red, like in neutral, then sometimes not go into 4-Hi, or maybe stay in 4-Hi and not go into 2-Hi right away. From what I recall, I disconnected the battery or something and the system reset and worked fine ever since.
Until this month. First, it wouldn't go into 4-Hi. It would only stay in 2-Hi. The red neutral light came on one time, but mostly it would just stay in 2wd, and when I'd push 4-Hi that light would flash for a while but it would never go into 4-Hi. It also wouldn't go into Auto (that light would flash, too, when I pushed Auto, and sometimes it would stay on Auto for a few minutes, but it wouldn't really go into Auto).
btw, when I start the truck, all of the 4WD switch lights come on, so I know they are good.
I drove the truck in some pretty good snow last week. While going through a snow drift, I pushed the 4-Hi button. It shifted into 4-Hi. And now it will not come out of 4-Hi!! It is stuck in 4WD.
I have read lots of forums about this. Here is what I have tried:
1. I pulled the TREC fuse for about a minute. The fuse itself is good. This didn't help at all. I've done this on two different occasions now. I also pulled and checked a bunch of other fuses.
2. I disconnected the battery for 45 minutes. It didn't help at all.
3. I pulled the dash trim and removed the 4WD selector switch. I took it apart to check for bad solder joints I could fix (per many forum posts I've read). I am unable to remove the circuit board from the plastic back of the switch (the pins go through the plastic and won't pull out). I'm assuming the soldering mentioned was on that backside, because there's not much to see on the front side. I reassembled the whole thing and put it back in. It still acts exactly the same. It is in 4-Hi. If I push 2-Hi or Auto or 4-Lo, they flash but it won't go in. Well, occasionally, it has always lit up the Auto light like it went into Auto, but it didn't really, and eventually the light goes back to 4-Hi. I have tried shifting while in Drive, while in Neutral and rolling, while and after backing up, also with the engine off, in neutral, brakes on--everything I've read to try. Nothing helps.
4. I am thinking about replacing the transfer case motor encoder ring. There is a good video of doing that here: Transfer Case C0327 - YouTube
Does anyone know if you really have to reflash the program? Another GM PIA.
How do I know if it's the 4WD selector switch or the encoder ring?
I can't find the 4WD selector switch on NAPA or AutoZone websites. Anyone have the part number? The switch is on eBay (with multiple part numbers), but I'd like to buy it, try it, and if it doesn't help, return it immediately and buy the encoder ring (I guess).
I know some posts refer to a TSB and to reading the powertrain codes, but from what I've read the C0327 code basically just say "it's not working" and doesn't really tell you what to fix. Also that many posters say when they take it to a dealer, they are usually told it's throwing too many codes to help anything. Great.
If you have any thoughts, experience, advice on this, I would greatly appreciate it. We need this truck for my wife to drive to work, and I don't want it driven on dry pavement very long like this, or it will probably tear up the drivetrain.
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I read the "Chevy electric non-auto 2 speed 4WD diagnostics" which I will attach page by page as JPEG files because of the very small filesize limits on this forum (I can't attach the 10 page PDF file!).
The problem is that I think "non-auto" means just that--no Auto setting, so it doesn't apply to my Tahoe. I don't even know what vintage GM trucks this document applies to... I found it in one of the thousands of online posts about GM 4WD problems (that should've been my first clue about buying this thing!). My data link connector pin 13 does not appear to have a pin in it, just the plastic housing. I tried grounding that slot anyway, in case my eyes were playing tricks on me--nothing.
Based on all I've read and heard, by the 2004 model the 4WD dashboard switches usually aren't the problem. I picked up a used transfer case motor. It only cost a little more than a new encoder ring and I don't feel like messing with opening the motor up. BUT, I can't get the old one off. What the guy in the video fails to mention is that the front driveshaft has to be turned just right to have clearance to pull the one bolt (STUPID GM DESIGN--AGAIN). My truck is stuck in 4WD, so the front DS doesn't turn by hand. And of course every time I run it up the ramps the DS isn't quite in the right spot. I'm trying to drop the front DS and can't get it, probably because of the tension in the system. I have the clamps pulled on the front u-joint. I cannot get the driveshaft to slide back into the transfer case. I've tried prying gently and tapping a hammer on a block of wood against the DS... nothing. How do I get this DS off?
Never mind, I finally got the transfer case motor replaced and that was the problem. I gave up on the driveshaft. Moved the truck back and forth a little on the ramps until things were lined up enough to get that one bolt out. What a terrible design. The old encoder motor looked like it was mounted crooked. Two of the bolt ears on the casting had broken off. Dirt was packed between the motor housing and the transfer case housing. The spline wsn't engaging enough to shift. It's not that easy getting the new one all lined up, engaged and getting the bolts started with the little room there is to work. For others that might be doing this, remember to turn the splined shaft on the transfer case to match the angle of the splines on the new motor. Don't try to turn the motor angle, because it has the encoder ring in it. I love this truck when it's working, but whenever I work on GM trucks I swear, no more for me.