"Chassis stabilization" and "Rear diff lock" errors

[afadeev]

Folks,
I'm debugging a recurring set of errors that are popping up on my '15 F80 M3:
- Chassis stabilization: Drive moderately
- Rear axle differential lock

Both were sporadic at first, but became more frequent over the summer.
I took it in for dealer diagnostics the other day, they flagged:
- LR (left-rear) pulse generator (part # 34526869322)
- Diff Servo motor (part # 33142284191)

I authorized replacement, picked the car up with cleared codes and all smiles.
A day and ~50 miles later, both error messages came right back.
@#$%.


Car is driving fine (I did not really push it on the street to test ABS and DSC, or lack thereof).

Dealer was very apologetic, offered to re-investigate on their dime.
Before I take it back, does this at all sounds familiar to anyone?

I ordered codes scanner, and among a slew of systems it can't read, it is showing fault with LF (left-front) speed sensor. Nothing on the diff.

Any chance an erratic speed sensor can cause diff error?


TIA,
a

P.S.: Here is the OBDII code scanner I was using: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[Crispy0001]

Yes, a faulty wheel speed sensor will throw up those errors. It's actually very common, replace the wheel speed sensor erase fault codes and should be fine.

[rmanm4]

Originally Posted by Crispy0001

Yes, a faulty wheel speed sensor will throw up those errors. It's actually very common, replace the wheel speed sensor erase fault codes and should be fine.

The dealership already replaced it, that is what a pulse generator is.

Since you already paid the dealership, get them to fix it. It's definitely sounds like a speed sensor issue, let's hope they put in a new (good) one!

[overlook637]

I had this issue last week.

1- when it says drive carefully. Listen to it. Every part of the stability system including the electronically controlled rear diff will not work and or not work safely. I had one tire spinning pretty good on acceleration from a stop and then the rear diff must had warmed up and provided some power to the other wheel. Sending the car sideways, harshly.

2- when i replaced the wheel speed sensor, i noticed the sensor had a good amount of metal powder and road crude on it. I had already drove 4 hours to get a sensor, so I replaced it. I bet all that was needed was to wipe off the metal crude. These sensors are just magnetic tone sensors. They should never go bad. I sprayed some brake cleaner down the hole and all around the brake area. This weekend I plan on inspecting / cleaning the other three wheel speed sensors.

[overlook637]

Originally Posted by Crispy0001

Yes, a faulty wheel speed sensor will throw up those errors. It's actually very common, replace the wheel speed sensor erase fault codes and should be fine.

It shouldn't be common for most vehicles. But, it appears to be common on these models.

I would suggest it be part of a 30k service, to clean and wipe off the debris that has been attracted to the magnetic part of the sensor. On the rear axle it is only a single torx bolt. Pull, wipe, replace, install bolt. Takes longer to gather tools, jack from the garage, and remove the wheels. I spent more time cleaning the inside of the wheels and inside of the tire wheel area.

A garage with a lift might be able to clean the sensor without removing the wheel.

[OnlyGerman]

Typical dealer replacing unneeded parts due to their incompetent techs

[afadeev]

Originally Posted by Crispy0001

Yes, a faulty wheel speed sensor will throw up those errors. It's actually very common, replace the wheel speed sensor erase fault codes and should be fine.

OK, thanks for the lead!

Originally Posted by rmanm4

The dealership already replaced it, that is what a pulse generator is.
Since you already paid the dealership, get them to fix it. It's definitely sounds like a speed sensor issue, let's hope they put in a new (good) one!

That's the thing - the last sensor they replaced was LR. 1 down, 3 to go.
The one that is throwing faults now is LF. I can make it 2 down, 2 to go?

Originally Posted by Crispy0001

Yes, a faulty wheel speed sensor will throw up those errors. It's actually very common, replace the wheel speed sensor erase fault codes and should be fine.

Originally Posted by overlook637

1- when it says drive carefully. Listen to it. Every part of the stability system including the electronically controlled rear diff will not work and or not work safely. I had one tire spinning pretty good on acceleration from a stop and then the rear diff must had warmed up and provided some power to the other wheel. Sending the car sideways, harshly.

Yep, I can positively confirm that both ABS and DSC are off, and rear diff are acting funny.
I am usually comfortable driving in DSC OFF mode (though usually not on the street), but with the diff acting somewhat unpredictably, this is little more squirrely than ever. For those of us who had learned driving on cars without any form of Traction Control, driving without DSC is not the end of the world ;-).

So really, if it's +1 sensor, I might throw some more money at the dealer to do one more corner. Just because the weather is super nice, and by the time I get the parts and get to work on it myself, it will be the next weekend, at the earliest.

Thanks, gents, I will report on what happens next.

a

[overlook637]

The sensors most likely just need wiped off.

[afadeev]

Originally Posted by OnlyGerman

Typical dealer replacing unneeded parts due to their incompetent techs

Indeed.
It's been years since I had to do something to the M3, so I made the mistake of outsourcing troubleshooting and remediation to the dealer. My bad. 100% my fault.


Solution was buying a BMW code scanner (link above), and DIY-ing the troubleshooting.
It was a failing FL (front left) ABS / speed sensor.

Technically, dealer (BMW of Morristown) may not have been wrong in having replaced the LR (left rear) speed sensor before. It probably also failed and needed replacement, as they claimed. The fact that 2 would go out in short succession is a bit unusual, but not impossible.
The fact that they bent me over the barrel for Diff Servo motor replacement is uncool and was a total waste. But again, my own fault for putting trust into them in the first place.

Originally Posted by Crispy0001

Yes, a faulty wheel speed sensor will throw up those errors. It's actually very common, replace the wheel speed sensor erase fault codes and should be fine.

Replacing LF sensor and resetting the errors did the trick.
I have not fully re-initialized all the computers by driving XX miles over YY ignition cycles yet (IIRC it takes >50 miles), but so far, car is back to its 100% fun self.

Originally Posted by overlook637

The sensors most likely just need wiped off.

I had checked all 4 sensors (3 old + 1 new), and old ones looked surprisingly clean. No debris on the tips.
I wiped them anyway, reset the lights, went on a test drive, codes came back.

BTW, the front vs. rear ABS / speed sensors are actually different part #s.
Don't ask me why BMW couldn't use the same sensor on all 4 corners, but if you need to replace yours:

front axle part #: 34526869320
rear axle part #: 34526869322

Both are ~ $45 from FCPEuro.com, or $175-280 from dealer parts departments. None of the 5 local dealer parts departments had one in stock, so I ordered from FCPEuro. Got it in my hands within 3 days of placing the order.

https://www.fcpeuro.com/products/bmw...te-34526869320

HTH,
a

[OnlyGerman]

Originally Posted by afadeev

Indeed.
It's been years since I had to do something to the M3, so I made the mistake of outsourcing troubleshooting and remediation to the dealer. My bad. 100% my fault.


Solution was buying a BMW code scanner (link above), and DIY-ing the troubleshooting.
It was a failing FL (front left) ABS / speed sensor.

Technically, dealer (BMW of Morristown) may not have been wrong in having replaced the LR (left rear) speed sensor before. It may have failed, as they claimed.
The fact that they bent me over the barrel for Diff Servo motor replacement is uncool and was a total waste. But again, my own fault for putting trust into them in the first place.

Replacing LF sensor and resetting the errors did the trick.
I have not fully re-initialized all the computers by driving XX miles over YY ignition cycles yet (IIRC it takes >50 miles), but so far, car is back to its 100% fun self.

I had checked all 4 sensors (3 old + 1 new), and old ones looked surprisingly clean. No debris on the tips.
I wiped them anyway, reset the lights, went on a test drive, codes came back.

BTW, the front vs. rear ABS / speed sensors are actually different part #s.
Don't ask my why BMW couldn't use the same sensor on all 4 corners, but if you need to replace yours:

front axle part #: 34526869322
rear axle part #: 34526869320

Both are ~ $45 from VCPEuro.com, or $175-280 from dealer parts departments (none of the local 5 locations had one in stock).

https://www.fcpeuro.com/products/bmw...te-34526869320

HTH,
a

Yup, diagnosis of issues before going will definitely help, whether it is bimmerlink or ISTA.

[afadeev]

Originally Posted by OnlyGerman

Yup, diagnosis of issues before going will definitely help, whether it is bimmerlink or ISTA.

Well, I celebrated too soon - the plot continues to thicken!

For those who are keeping the count - so far:
Step 1: read the codes, find what ABS / speed sensor is throwing error codes.
Step 2: LR and LF ABS / speed sensors have been replaced.
Step 3: Lights are reset.
Step 4: I go on my merry way, ~50-100 miles later the lights pop back up.


I am back to Steps 4->1.
This time around, it's the RF sensor that is tripping the same error codes.
Really?

What are the chances that all four speed sensors are dropping dead on me, one after the other?

I've ordered two more, for the right-side, will replace them all.
Somehow, I don't get the warm and fuzzy that that will be the end of this story!?

[Laostuh]

I get the chassis stabilization almost everyday, it goes away after turning off the car and turning it back on. Would this be covered under warranty? Might take it in before my warranty expires.

[Shubacca]

Are they bad sensors or dirty ones? It would make sense that if one was contaminated or dirty that the others could be too.

[afadeev]

Originally Posted by Laostuh

I get the chassis stabilization almost everyday, it goes away after turning off the car and turning it back on. Would this be covered under warranty? Might take it in before my warranty expires.

Mine is MY'15, long out of warranty.
If you are still covered, do take it in and let them swap parts blindly at BMW NA's expense. See post #1 about taking it to the dealer.

Originally Posted by Shubacca

Are they bad sensors or dirty ones? It would make sense that if one was contaminated or dirty that the others could be too.

I had removed and cleaned all 3 (4th one has already been replaced by the dealer).
None were dirty. At all.
They are screwed into the fully enclosed space between the inside of the rotor and wheel hub. While it's not impossible for dirt to get in there, it's neither likely, nor expected.

The one that was known to be generating faults (LF) was replaced by me, the fault went away on that corner.
Fault came back on another corner (RF).

I do find it peculiar, but the exact error message read as follows (old errors for LF, new ones are identical for RF):

[rmanm4]

These sensors are compared to each other by a module, this is how it calculates slippage and allows the traction control to do its thing. If one sensor is NEW and the other old ones are not as accurate then module freaks out. It seems like once one goes you need to replace all 4, just like when you do spark plugs or coils, its best to replace all of them at the same time!

[overlook637]

Originally Posted by rmanm4

These sensors are compared to each other by a module, this is how it calculates slippage and allows the traction control to do its thing. If one sensor is NEW and the other old ones are not as accurate then module freaks out. It seems like once one goes you need to replace all 4, just like when you do spark plugs or coils, its best to replace all of them at the same time!

Inductive wheel speed sensors encase a wire coil around a magnetically polarised core and operate in tandem with a pulse wheel mounted on a component rotating at wheel speed, for example, a driveshaft or hub. As the pulse wheel passes the sensor, the sensor’s magnetic field is disturbed, which induces an oscillating voltage within the wire coil and the circuit connected to it. The quicker the wheel rotates, the greater the magnetic field disturbance, the greater the induced voltage amplitude and the faster the oscillation frequency.

They should never fail and they are not a wear item. They are nothing at all like a spark plug.
Wheel speed sensors and their pulse rings are exposed to the atmosphere and have to operate under conditions of constant vibration and movement. As such, common faults are:

Sensor signal failures, caused by chafed or fractured circuit wiring, sensor or connector corrosion, or incorrect sensor fitment.

Pulse wheel related problems arising from corroded or damaged teeth, incorrect pulse ring fitment (misalignment), contamination from a build-up of ferrous material, or an excessive air gap between the sensor and the pulse wheel.

Are those $45 sensors OEM or a generic item?

When you inspected and cleaned the wheel speed sensors, did you spray cleaner down into the port holes? I emptied a can of brake cleaner in the speed sensor whole and around the entire brake area.

After cleaning the area, installing a new BMW sensor and clearing the code I had no further issues. It does seam like I get a flash on the traction control light on acceleration and turning briskly. I will clean the right sensor and sensor hole this weekend.

[rmanm4]

Originally Posted by overlook637

Inductive wheel speed sensors encase a wire coil around a magnetically polarised core and operate in tandem with a pulse wheel mounted on a component rotating at wheel speed, for example, a driveshaft or hub. As the pulse wheel passes the sensor, the sensor's magnetic field is disturbed, which induces an oscillating voltage within the wire coil and the circuit connected to it. The quicker the wheel rotates, the greater the magnetic field disturbance, the greater the induced voltage amplitude and the faster the oscillation frequency.

They should never fail and they are not a wear item. They are nothing at all like a spark plug.
Wheel speed sensors and their pulse rings are exposed to the atmosphere and have to operate under conditions of constant vibration and movement. As such, common faults are:

Sensor signal failures, caused by chafed or fractured circuit wiring, sensor or connector corrosion, or incorrect sensor fitment.

Pulse wheel related problems arising from corroded or damaged teeth, incorrect pulse ring fitment (misalignment), contamination from a build-up of ferrous material, or an excessive air gap between the sensor and the pulse wheel.

Are those $45 sensors OEM or a generic item?

When you inspected and cleaned the wheel speed sensors, did you spray cleaner down into the port holes? I emptied a can of brake cleaner in the speed sensor whole and around the entire brake area.

After cleaning the area, installing a new BMW sensor and clearing the code I had no further issues. It does seam like I get a flash on the traction control light on acceleration and turning briskly. I will clean the right sensor and sensor hole this weekend.

Induction resistance changes overtime. Usually heat will cause the core or wiring material to have different electrical resistance. Alternators are prime example of this on older cars without good voltage regulators, as the material changes due to heat, the current it creates fluctuates. Anything with induction coils will drift away from tolerance window overtime and it's usually due to heat cycles!

[overlook637]

Heat from what exactly? I've never tracked, raced, or done a burnout. No reason at all for a $200 wheel speedsensor on a 5 year old car to fail. My parents have near 250k miles on a 25 year old chevy truck that has never needed a wheel speed sensor. I've owned over a dozen cars, including some that have seen track time, and never needed a wheel speed sensor. I've warped brake rotors from excess heat on track use and that car didn't need wheel speed sensors.

[rmanm4]

Originally Posted by overlook637

Heat from what exactly? I've never tracked, raced, or done a burnout. No reason at all for a $200 wheel speedsensor on a 5 year old car to fail. My parents have near 250k miles on a 25 year old chevy truck that has never needed a wheel speed sensor. I've owned over a dozen cars, including some that have seen track time, and never needed a wheel speed sensor. I've warped brake rotors from excess heat on track use and that car didn't need wheel speed sensors.

Who knows! Im just spitting out what I learned in University from when I got my EE degree. The heat could be from location of sensor with respect to rotors, or from environment. I've replaced a few on older BMWs ive owned (8-10 years).

[overlook637]

Originally Posted by rmanm4

Who knows! Im just spitting out what I learned in University from when I got my EE degree. The heat could be from location of sensor with respect to rotors, or from environment. I've replaced a few on older BMWs ive owned (8-10 years).

I've never tracked the car to have heat created from braking. I doubt most of these failures are from owners who track race the cars.

My guess is the environment, in that the sensors are open and allowed to get very dirty. I would guess BMW designed the sensor location with a opening to keep them cool, which makes the open for road dust. That's what I learned working under the shade tree with my community college degree.

[afadeev]

Originally Posted by overlook637

Heat from what exactly? I've never tracked, raced, or done a burnout. No reason at all for a $200 wheel speedsensor on a 5 year old car to fail.

I have tracked my car, as I've done with all my bimmers for 20+ years, but that's still not a reason for speed sensors to fail.

Technically, I don't know that they've actually failed. Maybe the first one failed, or maybe its resistance reading went outside of some error bounds. Then the the resistance from its replacement turned out to be different enough for on board diagnostics to declare a fault with the next sensor it checked. Errors cascaded as follows: LR (replaced) -> LF (replaced) -> RF (now I replaced all right-hand-side sensors).
Now that I've replaced all 4 ABS sensors and reset the fault codes, the lights have stayed off for 100+ miles. Which is a very welcome development.

Originally Posted by overlook637

My parents have near 250k miles on a 25 year old chevy truck that has never needed a wheel speed sensor. I've owned over a dozen cars, including some that have seen track time, and never needed a wheel speed sensor. I've warped brake rotors from excess heat on track use and that car didn't need wheel speed sensors.

Same here.
The oldest bimmer I ever owned (E30 325i) was sold long time ago with 258K miles, with the original engine, tranny, diff, and all 4 ABS sensors and all other primitive electronic components working just fine. It did have many relays, light bulbs, and timing belts replaced, though. I've owned every 3-series generation since then, usually more than one sample. Never had ABS sensors fail on any of them.
But there is always the first time.

Originally Posted by rmanm4

Induction resistance changes overtime. Usually heat will cause the core or wiring material to have different electrical resistance.

I really like this theory.
The other possibility is that on-board diagnostic computers' sensitivity to resistance degradation over time is set to a too low of a threshold. That, plus the functional inter-dependency on the ABS sensor inputs is ridiculous - I was resetting error codes on DSC (stability control), chassis stabilization, drive-train malfunction, rear diff management (even from a front sensor error?!?!), interior ABS restraints (why?!), and 2-3 other in-vehicle systems that I can't recall right now.

It's a simple sensor failure mode that sends car's entire electronics ecosystem into the tail spin!

I have noticed an increased electronic fragility creeping in into the newer BMWs, over time.
This maybe another example of that.

a

P.S.: Big THANK YOU to everyone who responded to this, and shared their experiences on prior threads. The BimmerPost community is way more insightful, logical, and experienced than any and all BMW dealer techs!

[rmanm4]

Originally Posted by afadeev

I have tracked my car, as I've done with all my bimmers for 20+ years, but that's still not a reason for speed sensors to fail.

Technically, I don't know that they've actually failed. Maybe the first one failed, or maybe its resistance reading went outside of some error bounds. Then the the resistance from its replacement turned out to be different enough for on board diagnostics to declare a fault with the next sensor it checked. Errors cascaded as follows: LR (replaced) -> LF (replaced) -> RF (now I replaced all right-hand-side sensors).
Now that I've replaced all 4 ABS sensors and reset the fault codes, the lights have stayed off for 100+ miles. Which is a very welcome development.



Same here.
The oldest bimmer I ever owned (E30 325i) was sold long time ago with 258K miles, with the original engine, tranny, diff, and all 4 ABS sensors and all other primitive electronic components working just fine. It did have many relays, light bulbs, and timing belts replaced, though. I've owned every 3-series generation since then, usually more than one sample. Never had ABS sensors fail on any of them.
But there is always the first time.



I really like this theory.
The other possibility is that on-board diagnostic computers' sensitivity to resistance degradation over time is set to a too low of a threshold. That, plus the functional inter-dependency on the ABS sensor inputs is ridiculous - I was resetting error codes on DSC (stability control), chassis stabilization, drive-train malfunction, rear diff management (even from a front sensor error?!?!), interior ABS restraints (why?!), and 2-3 other in-vehicle systems that I can't recall right now.

It's a simple sensor failure mode that sends car's entire electronics ecosystem into the tail spin!

I have noticed an increased electronic fragility creeping in into the newer BMWs, over time.
This maybe another example of that.

a

P.S.: Big THANK YOU to everyone who responded to this, and shared their experiences on prior threads. The BimmerPost community is way more insightful, logical, and experienced than any and all BMW dealer techs!

YUP....it seems the code in the monitoring module compares all 4 sensors. This is probably crucial for TC to be so precise! Overtime all 4 modules degrade evenly and probably last a long time. But lets say one sensor goes bad for whatever reason, if it gets replace with a new one.....now you have the other 3 old sensors at different impedance and now the module is just not smart enough to compensate. BMW probably cant code some variation in the reading to allow for difference between sensors as it would effect TC too much!