AWD (old truck) vs 4WD (new truck)

[mjwills]

Hi all -

I came out of an Escalade ESV (05 Platinum) to a 2011 Yukon XL 2500. Is 4 auto the same as AWD? When I am in 4Auto I can feel it engage and works when in snow, etc. But when it is not slick or anything, it still feels engaged - should it feel like its back in 2WD when not really in use? Is this normal and will feel different than AWD?

Side note, but what is a way to test to make sure it really is in 4Auto vs 4Hi, I don't always trust computers and dials

 

[07Burb]

no...AWD and Auto 4x4 are two very different things. I'm going to assume that when you feel like it's engaged in 4x4 is around corners or lose gravel or something?

Also to answer youg last question, if your dial is turned to Auto 4wd and the light for that is illuminated it's in auto 4wd but could jump into 4 Hi at any moment at the whim of the computer because that's the purpose of auto 4wd.

 

[mjwills]

Thanks for the reply. For a recent example - today driving in the snow in 4 auto, I was on a side street and felt it engaged on the ice/snow. Then while getting the main road which was still wet but not slick, I still felt a vibration like something was engaged and turning (not turning corner but rotation). Once I flipped it to 2WD it went away. Maybe the computer felt it still needed to be in 4WD? That is why I was asking if there is a physical way to test if 4 auto is working correctly.

Is there something engaged when in 4 auto and that is when it feels different than 2WD? Maybe this is a better example - if driving on a dry road and put it in 4 auto, is something engaged?

 

[07Burb]

when in auto 4wd if driving normally and heading straight nothing should be engaged and should be like 2wd. With that said, if the computer feels any slippage at all it'll engage 4 Hi. This is why I am always in 2wd unless absolutely necessary not to be. I like to control what I'm in and do not like to relinquish that control to a computer.

So it sounds like yours is working as it should. when you rely on a computer to make decisions like if you should be in 4wd or not then you'll have times like you've described and not be real pleased with it's choice.

 

[NathanJax]

Here's a thread where they go into more about it...

http://www.tahoeyukonforum.com/forum/showthread.php?t=65396

 

[mjwills]

Thanks for the replies.

So driving on a dry road today, I put it in 4 Auto and I feel a clunk and then feel additional feedback in my feet. Goes away if I switch back to 2WD, and seems to go in/out when in auto. Seems like auto is always going to 4WD? I assume the additional feedback in 4WD is normal?

 

[07Burb]

I've never felt the need to put in Auto 4wd under dry conditions so I'm not sure what you're supposed to feel. My question for you is why would you feel the need to use Auto 4wd when you're not in a circumstance when 4wd will be even remotely necessary?

Like I stated yesterday, you're in Auto 4wd so that computer is going to constantly be searching for reasons to engage 4wd whether it's necessary or not. That thumping you're feeling is it engaging the transfer case and if you're in dry conditions it's doing this unnecessarily therefore putting extra wear and tear on your 4wd components. With that, it is detrimental to those components (and can cause catastrophic damage) to be engaged unless needed.

 

[Clean07Burb]

I've never felt the need to put in Auto 4wd under dry conditions so I'm not sure what you're supposed to feel. My question for you is why would you feel the need to use Auto 4wd when you're not in a circumstance when 4wd will be even remotely necessary?

Like I stated yesterday, you're in Auto 4wd so that computer is going to constantly be searching for reasons to engage 4wd whether it's necessary or not. That thumping you're feeling is it engaging the transfer case and if you're in dry conditions it's doing this unnecessarily therefore putting extra wear and tear on your 4wd components. With that, it is detrimental to those components (and can cause catastrophic damage) to be engaged unless needed.

This. Don't use 4WD or 4AUTO unless the conditions call for it. And I agree with 07Burb. I've never used the AUTO feature, so I can't say how it feels. I, too, like to control when 4WD engages/disengages, and which 4WD mode I want to be using.

 

[mjwills]

To answer the question of why would I put it in 4 Auto when conditions don't necessarily call for it? A couple reasons - 1) to see if putting it Auto is working properly or just going right to 4WD regardless of what the dial says it is in. 2) My understanding of Auto is that you can leave it in there all the time if you want to and 4WD only kicks in if needed. I believe the manual even says 4auto is fine to run all the time; I am trying to figure out if what I hear and feel is normal. Below is what I pulled from another site:


AUTO 4WD: The front axle engages and the transfercase engages 4wd. BUT, there is a Clutch Pack that also comes to life at this point and it controls how much power goes to the front axle. So under normal driving it will be dis-engaged and if the rear axle starts to slip it will start sending power to the front axle to compensate. It can mechanicly send anywhere from 10%-50% of the power to the front axle.

So, it sounds like you are in 4wd because the front axle is engaged and the drive shaft is spinning but, no power is going to it... yet... And yes, you will see a MPG drop in Auto 4wd mode...

4WD Hi - Lo: Front Axle is engaged, transfer case is engaged and power is sent 50-50 to the front and rear. NEVER use this mode on the street!!!