Just what the title says: 2015 Chevy Duramax 3500, discovered it had been in 4Hi for…a few weeks?? It is not our ‘daily driver’ and most often, my DH uses it for quick trips, otherwise it sits unused for two weeks at a time or so. But it definitely was driven at freeway speed during this time. I (we) feel stupid and angry that we didn’t seem to notice! It seems ok…but can anyone shed light on what, if any, damage we’ve done to our big boy!
I think it’ll be fine but I don’t really know. Is it driving normally now without being in 4 Hi?
What’s freeway speed to you? 65 mph? 75 mph?
It’s probably fine.
I do sometimes forget I left the pickup in 4WD but I can always tell when I go to turn. It sounds different and turns harder in 4WD. I notice that, and then it prompts me to look. (Of course, our new pickup also has it lit up on the dash that it’s in 4WD so that’s helpful too.) So that is something you can test yourself so you can learn to recognized the next time it is accidentally left in 4WD.
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More or less. I know it needs new tires, it has a bit of a shimmy on front at times and we are addressing that.
I’m surprised it drove at all in 4wd on normal pavement. Used to be a truck in 4wd would start ‘bucking’ if it didn’t have the surface slippage.
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Isn’t there a light display on the dash ( idiot lights - no offense intended) that show 4WD when it is engaged?
I’ve driven ours unknowingly with the hubs still locked ( manual locking hubs) but it hasn’t seemed to hurt it and at 23 it is still going strong.
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My idiot light is hidden behind the shifter on the steering column. 
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I had a 1979 International Scout with manual everything, including manual hubs. I would often have to transition from snow covered roads to bare freeway, and I was too lazy to pull over, shift out of 4High, and turn the hubs. As far as I know, it never caused a problem other than impacting my gas mileage, which was already abysmal with an eight cylinder/four barrel carb.
Rebecca
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Oddly, no, there’s no ‘idiot light’ on the dash, just a small knob located to the left of the steering wheel, where it can get whacked if you grab at the door frame when you slip getting in…ask me how I know! It’s automatic, no need to get out and turn hubs (yay for modern technology!).
It drove normally and turned normally, honestly. I’m wondering if maybe the knob was turned but the truck never actually was in 4WD?? I’ve driven it in 4Hi and 4low and the differences are dramatic compared to 2WD. So, maybe I have my answer!
Regardless, it’s going in for new tires (cha-ching!) and an oil change (cha-ching!) as well as her 50K service soon, so the big gray battleship will get a thorough going over. Thank you all for your replies. You’ve eased my mind somewhat.
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You’re probably fine. But…I am also surprised you didn’t feel it bucking on turns, so I’d be a little concerned it didn’t engage or is now broken.
Get thee to some mud or wet grass, put it in 4x4 and get a little stupid with someone watching to see if all 4 are breaking loose.
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I’ve been told that if a truck is left in 4WD too long, you’ll get “wind up” meaning it will feel bogged down when you’re driving it. I once pulled a new-to-me trailer home over icy Wyoming roads and was in 4H (2000 F-250) for quite a distance and never experienced this “wind up.” I think you’re fine.
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If it got turned on accident and not allowed to get into 4x, maybe? But it should have swapped the next time you stopped and started. I’d be more concerned your switch isn’t working right and you don’t have 4x when you need it 
I’d do this to dx it before taking it to the shop. Just to see.
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Update: I tested my 4x4 functionality yesterday-- it works! As I drove it around the gravel area by our house, in 4High, I could feel it ‘working’ in all four tires, and turning was a beyotch. That is not what I was feeling when I looked down while tootling down the freeway and noticed that knob was on 4Hi! So…when I talk to my service advisor I’ll mention this to them. Thanks again for all the info/help!
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Great news!!
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