Flashing DSC (4x4) Light on heavy acceleration.

[lichtman]

Originally Posted by wpoll

That small difference may be enough to cause the DSC to trigger under acceleration.

On xDrive cars, it's best to change all four tyres at the same time...

Thats good to know. The tires are legacy from the previous abuser of the vehicle, and have been pretty far down on my list of things that need attention. I guess if nothing else become readily apparent as the cause of this issue, they'll have jumped to the top of the list.

[andrewwynn]

are you able to get a snapshot of the values exactly when the car does it?

Test on a slippery surface like sand on gravel and see if you can reproduce the effect.

It’s actually pretty likely you are just getting wheel spin. Are you hitting the kickdown button at the limit of accelerator motion? If you are moseying around a curve in the typical situation of go under the bridge then left up the on ramp you’ll be in 4th. If you hit the kickdown the car will shift to second and the 3.0 can definitely break traction with old not awesome tires if there is just a little oily film from the cars before you.

I think you said you have x drive. Monitor the % to front. If the car is not putting enough torque to front, for sure, wheel spin.

[Fifty150hs]

Originally Posted by lichtman

Thats good to know. The tires are legacy from the previous abuser of the vehicle, and have been pretty far down on my list of things that need attention. I guess if nothing else become readily apparent as the cause of this issue, they'll have jumped to the top of the list.

They should definitely jump up on your list. Running mismatched tires like that front to rear can eat up your transfer case. There's a small difference allowed between the two, I don't remember how much, but it isn't much.

[andrewwynn]

Originally Posted by Fifty150hs

They should definitely jump up on your list. Running mismatched tires like that front to rear can eat up your transfer case. There's a small difference allowed between the two, I don't remember how much, but it isn't much.

I looked it up once I think it’s 1% max s
Differential.

2225 / ∏ / 2 = 354 mm radius so 354*.01=3.54 mm difference in radius between tires

3.54/25.4=0.139*32=4.448

So, if the tires are the same model a difference of 4-1/2 32nd is what is allowed on the x-drive.

Different model tires can easily have more than that difference off the shelf.

To measure the radius of the tire I would lift the corner and wrap some masking tape (doesn't stretch) around and Mark where It overlaps then move to the other tire make another mark for the other axle.

My tires are 255/55/18 and are calculated to be 2225 or so mm = 2225/25.4=87.598 in.

That's roughly 87-5/8"

87.6*0.01=0.876 inch difference in circumference allowed or 7/8"

So get a measurement. People on xo have had their transmission act funny due to differential in tire sizes.

At least rule out tire size as the culprit (or discover it might be the problem).

[jdstrickland]

I cannot believe that different brands of the same size tire is enough to confuse the system. If you have all 4 tires the same size, 265/75x18, whatever, then the car should be able to deal with any differences that come from manufacturing variations. My question about sizing was if the OP had tires that were actually different sizes, not different brands of the same size.

The system looks for all four tires to be rotating at the same speeds, but turning a corner demands that the outside tires turn faster than the inside -- the whole point of having a differential -- and if the tires front to rear are different sizes then the car is turning, the speed differences are accentuated and this might be enough to trigger the system activation. The flashing light means that the system is activated, the reported loss of power and the brake drag is a function of the activation of the system. All of the stuff reported is proper, except that the conditions are such that activation of the system is possibly not correct. All of the stuff reported is linked, and is doing what it is supposed to do. The problem is, it is doing it when it should be.

It's entirely plausible that the Steering Angle Sensor has lost it's home position, and the car is reacting to an extreme steering angle and a throttle position that is making the car fear for its life so it activated the Stability Control system. Before you do anything else, turn the steering wheel to full lock, then turn it to full lock in the other direction, then full lock again in the original direction. The computer will count pulses from lock to lock in order to know where home position is -- home will be straight ahead. You want to turn to full lock in a continuous motion without stopping.

[bcredliner]

Originally Posted by lichtman

Thats good to know. The tires are legacy from the previous abuser of the vehicle, and have been pretty far down on my list of things that need attention. I guess if nothing else become readily apparent as the cause of this issue, they'll have jumped to the top of the list.

Since purchasing my X5 new I have never replaced all four tires at the same time. I have almost always purchased two fronts or two rears at a time but there have been a few times when a tire couldn't be fixed that I purchased one tire when tread on remaining tire was about half of original depth. Never had a problem. From day one the rear tires have lasted less than half a long as the front.

[lichtman]

Originally Posted by jdstrickland

...The system looks for all four tires to be rotating at the same speeds, but turning a corner demands that the outside tires turn faster than the inside -- the whole point of having a differential -- and if the tires front to rear are different sizes then the car is turning, the speed differences are accentuated and this might be enough to trigger the system activation. The flashing light means that the system is activated, the reported loss of power and the brake drag is a function of the activation of the system. All of the stuff reported is proper, except that the conditions are such that activation of the system is possibly not correct. All of the stuff reported is linked, and is doing what it is supposed to do. The problem is, it is doing it when it should be...

We're on exactly the same page with that. The system is functioning exactly how it should, except possibly activating with no reason (bad data from one of the system inputs). I've calibrated my steering angle sensor with ISPA+, and swapped out the yaw sensor just to check. this morning I super carefully equalized all the tire pressures and reset the TPMS monitor (I'm not actually sure if the TPMS communicates with the DSC module but did it just to be safe). I'm about to head out and take it for a spin on the freeway. in answer to your earlier question all the tires are the same size 235/65-17.
I'll report back later with how it did.

Thanks again to everyone for all the input! You guys are awesome.

[andrewwynn]

235s much more likely to lose traction. I have a feeling you just are breaking traction and DSC is just doing its job..

[jdstrickland]

My X5 has 245/65x17. Andrewwynn might be onto something. If you're throwing the weight and balance to one side and hitting the gas hard, you can be spinning a tire and the DSC is doing it's job.

In the tire size numbers, 235 is the width of the tread. You have a skinny tire. You need to consider that you are driving in a manner that is causing the car to fear for its own life. It's not so important if you can cause the problem you report, it's important if you can avoid the problem you report.

[andrewwynn]

I know this all too well.

I bought my x5 with 255/55/18 Dunlop winter tires.

I was immediately accustomed to the capability of the tire.

We bought wife's x5 with "bargain basement" 235/65/17.

When I drove her car in snow it felt like a bad front drive. I had no sense of all wheel traction. When I took corners like I always do in my car, her car would under steer over steer do anything but track a radius. It also just handled like total crap.

I bought a new/ish set of Dunlop winter tires for my car but also a new set of rims so I put my rims and tires on her car.

Holy crap it was absolutely night and day difference! I thought the handing difference had more to do with mine having the sport suspension.

In a blast from the past. The first car I drove as a teen was an Impala and it had 235s until one day dad found a deal on some barely used 225s.

The very first time I stopped firmly at a yellow light I probably should have gone through, obstacle like instantly locked the brakes; not even close to the same amount of force I used daily.

I'm a little surprised if the 6 is pulling off this feat but I think the odds are in the fairly likely class.