Overenthusiastic traction control?

[enuff_zed]

If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?

There might well be 2 per axle. I read the BMW technical brief for the stability and traction control which mentions the sensors on each axle so that could have meant that there are 4 in total.

Fair enough. Thank you.

[ph001]

It's done from the ABS sensor ring - so one per wheel.

DSC is more complex than that though as it also takes inputs from throttle position, steering angle, yaw and longitudinal acceleration.

[Pbondar]

If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?

There might well be 2 per axle. I read the BMW technical brief for the stability and traction control which mentions the sensors on each axle so that could have meant that there are 4 in total.

According to the E89 BMW USA technical briefing document to help the various traction /stability states there are:

4 wheel sensors sensing speed of each wheel
A longtitudinal acceleration sensor
Front and rear ride height sensors
Yaw angle sensor
Rate of change of steering sensor
Steering torque sensor
Torque sensor on gearbox output
On 8 speed boxes torque sensor on gearbox input

Some of which are duplicated and ignoring any just used for electronic damping..

As others suggested with only rotational sensor per axle you could not easily verify a spinning wheel in a straight line

The ABS system works in tandem and automatically calculates/ corrects for asymmetrical wheel arrangements

From a design viewpoint it would be a waste of assets not to make use of the abs wheel sensors since they are already there ..

[R.E92]

If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?

There might well be 2 per axle. I read the BMW technical brief for the stability and traction control which mentions the sensors on each axle so that could have meant that there are 4 in total.

According to the E89 BMW USA technical briefing document to help the various traction /stability states there are:

4 wheel sensors sensing speed of each wheel
A longtitudinal acceleration sensor
Front and rear ride height sensors
Yaw angle sensor
Rate of change of steering sensor
Steering torque sensor
Torque sensor on gearbox output
On 8 speed boxes torque sensor on gearbox input

Some of which are duplicated and ignoring any just used for electronic damping..

As others suggested with only rotational sensor per axle you could not easily verify a spinning wheel in a straight line

The ABS system works in tandem and automatically calculates/ corrects for asymmetrical wheel arrangements

From a design viewpoint it would be a waste of assets not to make use of the abs wheel sensors since they are already there ..

The problem is that it doesn't adjust. Hence the plethora of topics across the likes of e90post stating that incorrect tyre sizes caused huge issues with traction control.
The E89 shares a platform with the E90 and has interchangeable control units and sensors.

If you upsize the tyres on one axle then the car will see the front wheels going at different speeds to the rear. It doesn't know the actual vehicle speed, it has to calculate it based off the wheels rotations.

[jamie_z4]

Or you could just read my post regarding the duff abs rings on page 1 which is also really common on e90 Post etc

[Pbondar]

R. E92..

I think you are wandering off the point...the OP has a bog stock 64 plate 20i auto E89....supplied by a main dealer and in warranty..

So he will have whatever bmw oem fitment wheels and tyres...so all within tolerances ...

Therefore your probable cause analysis was not valid given the car specifics..

In that context your original technical description was incorrect..

There may be issues arising from significantly asymmetrical set ups on E8x platforms...but that isn’t because there are only two wheel sensors...

The code that drives all these systems is not in the public domain so no one apart from BMW and their partners knows what hard and soft limits have been set up in the various computer systems..

The more I read how sophisticated and interlinked these myriad of systems are on the e89 the more wary I am of simple fixes or improvements that people suggest..

[flybobbie]

Perhaps it's just a broken wire that breaks when the wheels rise over the hump.
Try to see if just the front or rear sets it off.

[ph001]

My best guess would be dodgy yaw sensor or acceleration sensor. The yaw ones do fail on the E46 occasionally and it’s probably the same sensor.

[R.E92]

R. E92..

I think you are wandering off the point...the OP has a bog stock 64 plate 20i auto E89....supplied by a main dealer and in warranty..

So he will have whatever bmw oem fitment wheels and tyres...so all within tolerances ...

Therefore your probable cause analysis was not valid given the car specifics..

In that context your original technical description was incorrect..

There may be issues arising from significantly asymmetrical set ups on E8x platforms...but that isn’t because there are only two wheel sensors...

The code that drives all these systems is not in the public domain so no one apart from BMW and their partners knows what hard and soft limits have been set up in the various computer systems..

The more I read how sophisticated and interlinked these myriad of systems are on the e89 the more wary I am of simple fixes or improvements that people suggest..

My point is that he just needs to check his tyres out before jacking the car up for a full inspection. If OP has OEM tyre sizes and matching tyres across the axles then it's time to look elsewhere. Over active traction and stability control is something which people also notice when mixing runflat and normal tyres.

The problems I described are across the E89 chassis family. That includes the E89 Z4, all E9x 3 series models and the E8x 1 series models.
In fact having larger or smaller rear wheels is a problem on almost all cars with modern stability control systems.
I described an issue with mismatching tyres which perfectly fits the description and is present on all vehicles mentioned above. I don't know why this upsets you so much.

[Probocop]

I also think it's the ABS sensor. I had the same symptoms on my old E81 1 series. It progressed into the DSC flashing when turning (left or right depending on which sensor was bust)

[enuff_zed]

R. E92..

I think you are wandering off the point...the OP has a bog stock 64 plate 20i auto E89....supplied by a main dealer and in warranty..

So he will have whatever bmw oem fitment wheels and tyres...so all within tolerances ...

Therefore your probable cause analysis was not valid given the car specifics..

In that context your original technical description was incorrect..

There may be issues arising from significantly asymmetrical set ups on E8x platforms...but that isn’t because there are only two wheel sensors...

The code that drives all these systems is not in the public domain so no one apart from BMW and their partners knows what hard and soft limits have been set up in the various computer systems..

The more I read how sophisticated and interlinked these myriad of systems are on the e89 the more wary I am of simple fixes or improvements that people suggest..

My point is that he just needs to check his tyres out before jacking the car up for a full inspection. If OP has OEM tyre sizes and matching tyres across the axles then it's time to look elsewhere. Over active traction and stability control is something which people also notice when mixing runflat and normal tyres.

The problems I described are across the E89 chassis family. That includes the E89 Z4, all E9x 3 series models and the E8x 1 series models.
In fact having larger or smaller rear wheels is a problem on almost all cars with modern stability control systems.
I described an issue with mismatching tyres which perfectly fits the description and is present on all vehicles mentioned above. I don't know why this upsets you so much.

I think the basic premise is, (as implied by R.E92), to always check the easiest things first and discount them before diving into complicated, potentially expensive stuff.
Will only take 5 minutes to note the tyre sizes, stick them on the forum and get an answer.

[Pbondar]

[/quote]

I think the basic premise is, (as implied by R.E92), to always check the easiest things first and discount them before diving into complicated, potentially expensive stuff.
Will only take 5 minutes to note the tyre sizes, stick them on the forum and get an answer.
[/quote]

I think we all agree that fault diagnosis, especially armchair diagnosis is that it’s based on probabilities...

Therefore a new 3 month old owner of a car bought from a main stream bmw dealer under a full warranty will NOT be supplied with non OEM wheels and non OEM tyres...in all probability

Therefore for an armchair diagnosis without any detailed information from the patient you would assume that it is NOT a tyre/wheel issue based on it being supplied by bmw

Therefore the fault, if it is a fault, must, based on probability lie elsewhere... I

The issue with all BBs is that people leap in, shoot from the hip without reading the original post properly or follow the chain before replying...

Yes i’ve done it too..

[jamie_z4]

I also think it's the ABS sensor. I had the same symptoms on my old E81 1 series. It progressed into the DSC flashing when turning (left or right depending on which sensor was bust)

Finally someone with some common sense...

[enuff_zed]

I think the basic premise is, (as implied by R.E92), to always check the easiest things first and discount them before diving into complicated, potentially expensive stuff.
Will only take 5 minutes to note the tyre sizes, stick them on the forum and get an answer.
[/quote]

I think we all agree that fault diagnosis, especially armchair diagnosis is that it’s based on probabilities...

Therefore a new 3 month old owner of a car bought from a main stream bmw dealer under a full warranty will NOT be supplied with non OEM wheels and non OEM tyres...in all probability

Therefore for an armchair diagnosis without any detailed information from the patient you would assume that it is NOT a tyre/wheel issue based on it being supplied by bmw

Therefore the fault, if it is a fault, must, based on probability lie elsewhere... I

The issue with all BBs is that people leap in, shoot from the hip without reading the original post properly or follow the chain before replying...

Yes i’ve done it too..
[/quote]

Errr? So....are we violently agreeing

[Felixlamb]

It's more than likely the reluctor ring on the driveshaft. It's very well documented online and YouTube guides how to fix it, it's where the driveshaft rusts and bulges out the abs ring and it touches the sensor. It's happened to two of my z4s and is fixed by fitting new reluctor rings and new abs sensors if it's damaged them.

No need to disable a vital safety function which bmw provided in the first place, just get it fixed.

It's exactly that. Dropped it into Sytners this morning and they've just called me to say that's the issue. Apparently as it's corrosion it isn't covered under the 1 year warranty I got when buying the car...fun. (I only bought the car 3 months ago.) They said they're trying to contact BMW to get it done as a goodwill gesture, so fingers crossed.

The mechanic I spoke to said the corrosion was quite bad, and implied that it may have been there even before I bought the car from them, so kinda concerning that they didn't pick that up when they do their multi-point checks? She says it's not safe to drive.

If BMW don't budge, any idea of how much I'll have to part with to sort the issue out?