Auto 4WD strangeness, help me confirm my thinking

DocBrown

Well-Known Member
I got a 2016 Silverado Z71 LTZ 2 about a month ago. CPO and 37k. I don't think the previous owner ever had in snow or salt. This is a rust free truck. I mean, really rust free, which is phenomenal for any 5 year old vehicle in WI. The only rust is a little on the muffler. I also don't think the previous owner ever turned any 4WD mode on. This is my 3rd GM with 4WD. I typically don't use it except for snow that's more than a few inches or really icy conditions, and then it's Auto 4WD. I've used it twice in the past couple of weeks due to heavy snowfalls, 11 inches yesterday.

Typically in Auto you feel the back wheels start to slip then the fronts engage. It's pretty smooth. Several times in my 2016 with Auto on, when making a turn, or just turning the wheel part way, on snow I get crow hopping. As I straighten the wheel the hopping stops and it suddenly lurches forward. I'm thinking even though the knob says it's Auto 4WD, it's really in 4HI. That's how it's behaving. I've never had crow hopping with Auto in my other trucks. Thoughts? I'm going to make an appointment with the dealer since it's got a bumper to bumper warranty until next Jan., but I wanted to get some other thoughts on this.

That said, I'm batting 1000 with GM 4WD. I have not had one yet that just worked. My TB was in the shop several times, and my Sierra constantly had Service 4WD messages. Neither truck's 4WD ever worked reliably.

Thanks!
 

Mooseman

Moderator
I don't use auto, either in the TB or the Avy. I did just try it in the Avy just to see if all was working right but I can't say for sure if mine experienced the same behaviour as yours. Maybe it depends on how long it takes to disengage the front wheels. I know on the Saab, the AWD would disengage fairly quickly, I'd say, within 30 seconds.
 

TJBaker57

Well-Known Member
Could the age of the autotrak fluid have something to do with this? I thought in auto the TCCM engaged the front drive incrementally, such that there should be some slipping of the clutch pack that would prevent the crow-hopping?
 
OP
DocBrown

DocBrown

Well-Known Member
Could the age of the autotrak fluid have something to do with this? I thought in auto the TCCM engaged the front drive incrementally, such that there should be some slipping of the clutch pack that would prevent the crow-hopping?
That was my understanding. I was thinking about the age of the fluid too. My guess is due to low mileage it was never changed.
 

TollKeeper

Well-Known Member
I would bet that the steering wheel angle, or YAW, or wheel speed, sensor is off.

I only use A4WD unless its a lot of snow (like 12 inchs). I know my Voy is 12 years older than your truck, and it doesnt have all the gadgetry yours does. I can say, thats not normal operation, and would likely suggest using that CPO, and have them verify the wheel speed sensors, YAW, and angle sensors. Its detecting a slip, or bad angle, somewhere, and its trying to react to a situation that it doesnt need to react to... That is of course unless you are drifting your way around those corners on purpose, but it doesnt sound like it.
 
OP
DocBrown

DocBrown

Well-Known Member
I would bet that the steering wheel angle, or YAW, or wheel speed, sensor is off.

I only use A4WD unless its a lot of snow (like 12 inchs). I know my Voy is 12 years older than your truck, and it doesnt have all the gadgetry yours does. I can say, thats not normal operation, and would likely suggest using that CPO, and have them verify the wheel speed sensors, YAW, and angle sensors. Its detecting a slip, or bad angle, somewhere, and its trying to react to a situation that it doesnt need to react to... That is of course unless you are drifting your way around those corners on purpose, but it doesnt sound like it.
Naw, just normal acceleration. I mentioned the CPO because I'm planning to get it in, I just wanted additional thoughts. I really appreciate it!
 
OP
DocBrown

DocBrown

Well-Known Member
I talked to a dealer today, not the one I bought from because of the distance away, but one I've had good service from before. They said that doesn't sound right, like it indeed going into 4HI. I have an appointment to drop it off next Wed.

Thanks all!
 
OP
DocBrown

DocBrown

Well-Known Member
Just a follow up. The dealer says it operating normally, binding is normal when the wheel is turned, even in Auto 4WD if the system is engaged. So, it doesn't look like we're getting any more heavy snow, but next time I use the system I'll turn it off when turning corners.

That said they at least they didn't charge me anything.
 

Mooseman

Moderator
I'd still question their diagnosis. When the AWD is on but not engaged, the front and rear wheels are not connected to each other, which is the cause of binding or crow hopping. The front diff is an open design therefore they can rotate at different speeds, unless it's different on the later model trucks and have some sort of limited slip capability.

If this was normal operation, there would have been a bunch of people complaining about it on the AWD only trucks like the Saab, Rainier and Bravada. When you put it to 2wd, the disconnect disconnects the axle and this breaks the mechanical connection in the diff. Either your encoder motor isn't working right or the transfer case isn't disengaging. I'd jack it up on all fours and check what the front driveshaft does in 2wd, auto and 4hi. In 2wd, the driveshaft should not be moving, in auto, it won't move at first until it thinks there's rear wheel slippage and engages the TC to drive the front wheels. In 4hi, it should be turning right away.
 
OP
DocBrown

DocBrown

Well-Known Member
I don't disagree which is why I took it in. They said if the rear wheel is slipping while turning it's going to be engaged and the wheel hop is showing it's actually working as it's supposed to. When going straight I can't feel the wheels slip like I could on my '08 Sierra and my TB. But I know it's engaged because it just goes in the snow. I can get the tires 2 loose grip in 2wd and the traction control kick in, in the same snow. Makes me wonder if the system reacts quicker than the older ones. 8 years technology could be all the difference. This truck is so different than my old one. I've only put about 300 miles or so on it and still getting used to it.

I only used 4hi once on my TB when we got 14 inches of snow in less than 24 hrs that shut down SE WI. I ended up having to drive to work. If not for 4hi I would never have gotten there. Otherwise we just don't get enough to make it useful.

I've owned 3 2wd Suburbans. They are such heavy beasts I never needed 4wd.
 

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