4wd abs stabilitrak: are these all integrated systems?

[dig828]

Brief summary of main concern: abs stabilitrak issues (brakes self actuating on dry straight pavement while driving)::nono:

This situation presented itself only after the FIRST and subsequent use of 4WD....I had owned the vehicle for 3 months and didn't touch the 4wd selector switch until then, and since that time the trouble began....:confused:

Envoy spent 16 days at dealership; yaw sensor and EBCM eventuallly replaced. The vehicle SEEMS to be ok, however I have not yet moved the 4wd selector switch to see if this would matter....

could it? should it? are all these systems interconnected? Any help is appreciated, and thanks in advance!:)

[RayVoy]

could it? should it? are all these systems interconnected? Any help is appreciated, and thanks in advance!:)Yes, all 3 use the same sensors.

[Robert1101]

If you are not on dirt, ice, snow, etc make sure the road is very straight prior to putting it in 4wd. Do not turn with it in 4wd on dry or wet pavement. This can cause damage to different parts.

[dig828]

"Yes, all 3 use the same sensors.":tiphat

in re. above quote, and to repeat replaced parts so far, (yaw sensor and EBCM)....what other sensors, parts, etc may be the cause of this particular problem? I know there is a transfer case module....

just not sure how this all ties in....also what about the wheel sensor? I know the steering wheel position sensor(?) is also involved, thanks to spending countless hours on this fantastic source of information site....but that has been ruled out as a cause.

and I apologize if these are elementary questions but it's obvious these "new fangled" vehicles are not like they used to be.....this is not to be taken as a degrading comment.....but to me, simple is better....:m2: (especially when the SAFETY features malfunction!)

[RayVoy]

The 2008 trucks have 4 channel ABS, with a rpm sensor at each wheel (the earlier trucks (2005 and older) have 3 channels) Any difference in detected rpm of wheels will activate the ABS when braking.
Now that I think about it, only the older 2wd trucks had stabilitrack, they may have had 4 channel ABS.
When in 4AWD, the transfer case uses the rpm data to decide if front drive should be activated.
And, the stabilitrack feature applies a brake or 2 to keep the truck driving square to the road. This is also determined from the wheel rpm data.

[dig828]

"Any difference in detected rpm of wheels will activate the ABS when braking." OK, got it:thumbsup:

"When in 4AWD, the transfer case uses the rpm data to decide if front drive should be activated."....
This part not so much....how come only in 4AWD? not 4hi or 4lo?

so if I do test the reliablity of the fix by changing the drive selector and the problem (self actuating brakes while driving on dry pavement) returns, should a wheel sensor or transfer case mod be suspect? Probably both, huh?

any clue as to which one would be more likely to fail?

BTW, good info. :thx

[RayVoy]

Just to answer ur AWD question, when in 4HI, or 4LOW, the transfer case connects the front axle and the rear axle. When you select these positions, you tell the transfer case that "I want power at the front wheels now". When you select 4AWD, there is only power transfered to the front axle when slippage is detected. You are telling the transfer case, "I want power to the front axle, only when the rear wheels spin".
This spinning is detected by the sensors we have been talking about.

I would think, that if your brakes are self-applying (is that a word :undecided) there might be a problem with traction control.

[dig828]

"...there might be a problem with traction control."

Ok. So how many sensors are involved with this? Let's see, I know about the wheel (speed?) sensor, yaw rate sensor, and EBCM...the latter 2 have been replaced, so by process of elimination, I guess that leaves....WHEEL sensor?

Don't tell me.....there's more?:confused:

[RayVoy]

"...there might be a problem with traction control."

Ok. So how many sensors are involved with this? Let's see, I know about the wheel (speed?) sensor, yaw rate sensor, and EBCM...the latter 2 have been replaced, so by process of elimination, I guess that leaves....WHEEL sensor?

Don't tell me.....there's more?:confused:I didn't know we have yaw rate sensors. I know the expensive European cars have yaw sensors in their stability systems. I though our stability was just a fancy name for traction control.
When I was explaining the stability sensors in the earlier posts, I was thinking/talking traction control.
If we have true stability control, I apologize if I mis-lead you.

[dig828]

I know I had just regular traction control in my '04 TB;no button (that I ever knew of; NEVER had any problems in 4 years) to turn it off/on..... "stabilitrak" is definitely on my '08...I thought I read somewhere it was added in either '06 or '08?

:thxAnyway, thanks for the info. In case you're interested, I dug out the latest service repair order.

"Road test w/customer, verify concern. Called TAC assistance case# *****; Advised check all connections at yaw rate sensor, EBCM and all grounds.
Replace EBCM due to dump valves interm turning on, program new EBCM, reroad test several miles...trac is not engaging at this time, advise customer will need to be driven by customer to verify concerns,"

Still have not changed drive selector at this time, but I think I have convinced myself it's totally fixed:bonk:

[xsaosinnerx]

If you are not on dirt, ice, snow, etc make sure the road is very straight prior to putting it in 4wd. Do not turn with it in 4wd on dry or wet pavement. This can cause damage to different parts.

this confuses me, we are equipped with AWD... what is the difference then with AWD and 4WD?

If there is an issue with turning in 4wd, wouldn't it be the same issue as if it was in AWD?

[RayVoy]

this confuses me, we are equipped with AWD... what is the difference then with AWD and 4WD?

If there is an issue with turning in 4wd, wouldn't it be the same issue as if it was in AWD?Don't take this as a smart-ass answer, but if AWD and 4WD (4HI) were the same, we wouldn't have 2 selections on the dash switch.
4WD, better known as 4HI locks the front axles and wheels to the rear when the selection is made.
4AWD only locks the wheels and axles when slippage at the rear wheels is detected, in other words, there is "some" automatic functionality included.

[dig828]

Seems like I will be returning to dealer again. :worried:

Today's 8 mile round trip drive produced same problem at two different times, the final one and most intense traction control blinking light and definite front brake grab upon driving on a very small patch (less than 3'x3') of new fallen snow...

anyone care to comment? I thinking ....wheel sensor? but that's only 'cause I can't quite "get" the 'traction control' and/or 'stabilitrak" feature(s) and how each one is different, but for the same purpose..