Uncommanded acceleration 130i
Discussion
A few more occurrences of ABS warning plus dodgy speedo plus having been warned before that there was an error code from a ring sensor I'm pretty convinced it's that tbh. And I do have a non urgent appointment for it to be looked at.
But in the meantime I have had one other random piece of accelleration. Like the previous one it was just before the warnings came back.
Is there any kind of behaviour at all of DSC that could cause that, i.e. can it ever have a higher throttle setting than your foot? I cannot say for sure, btw, that the first one wasn't the throttle staying "stuck" on after a downchange as that is definitely what happened in the second one. So if the DSC can "sustain" a throttle setting even if the foot is off the throttle that would be sufficient for me to understand this.
It just doesn't feel like primarily a throttle problem. Certainly I'd be amazed if a ring sensor isn't fecked in some way, it's just the accelleration I'm really trying to understand.
But in the meantime I have had one other random piece of accelleration. Like the previous one it was just before the warnings came back.
Is there any kind of behaviour at all of DSC that could cause that, i.e. can it ever have a higher throttle setting than your foot? I cannot say for sure, btw, that the first one wasn't the throttle staying "stuck" on after a downchange as that is definitely what happened in the second one. So if the DSC can "sustain" a throttle setting even if the foot is off the throttle that would be sufficient for me to understand this.
It just doesn't feel like primarily a throttle problem. Certainly I'd be amazed if a ring sensor isn't fecked in some way, it's just the accelleration I'm really trying to understand.
Yeah that is odd- both my rear wheel speed sensors/reluctor rings went recently (E82 125i) and I had the usual cacophony of warning lights and loss of cruise, DTC/DSC and ABS, and then the loss of the speedo altogether (after the other one went almost immediately after) but there was never a hint of unintended acceleration.
The throttle did feel a bit weird admittedly, it was noticeably less smooth as you came off and on it but otherwise seemed normal. Other than that it drove totally normally (lack of electronic aids notwithstanding).
The throttle did feel a bit weird admittedly, it was noticeably less smooth as you came off and on it but otherwise seemed normal. Other than that it drove totally normally (lack of electronic aids notwithstanding).
I very much doubt that failure of a wheel speed sensor would result in the car applying the throttle, these sensors do fail, one has failed on my Z4C you get the ABS and DSC warnings but the car doesn't take off for the horizon, I doubt there would be much left of BMW if that was the case.
Is it a ZF8 Auto? If the transmission TCU doesn't know the road speed (due to bad ABS sensors), it can sometimes lurch into a higher gear which feels like unintentional acceleration. Or is it literally like the car keeps accelerating when you take your foot off the gas?
As said, need to hook ISTA up to it and get some codes and or monitor live data on the key sensors.
As said, need to hook ISTA up to it and get some codes and or monitor live data on the key sensors.
rottenegg said:
Is it a ZF8 Auto? If the transmission TCU doesn't know the road speed (due to bad ABS sensors), it can sometimes lurch into a higher gear which feels like unintentional acceleration. Or is it literally like the car keeps accelerating when you take your foot off the gas?
As said, need to hook ISTA up to it and get some codes and or monitor live data on the key sensors.
Nope, 6 speed manual. It literally accellerated with foot off accellerator, and it did it twice so I'm certain it's not me imagining it. It wasn't "foot to the floor" either, just to be clear - the second one was definitely just as if the accellerator was staying in the same position, and the first one may have been (took me by surprise too much to be sure). As said, need to hook ISTA up to it and get some codes and or monitor live data on the key sensors.
I'll report back once it's been looked at. Of course it's plausible that the two are totally unrelated and just coincidentally occuring at same time but doesn't feel like that.
Nah, mine doesn't have CC.
Another occurrence today - lasted enough time to comment on it to my passenger! This time it was 100% definitely maintaining the throttle setting I'd given it when changing gear, which was enough to take it to about 5500 RPM with the clutch down, so a sorta 1/3rdish throttle setting. And then the ABS etc lights all go back on again.
Anyway I won't keep updating thread until it's been looked at. But it's very odd.
Another occurrence today - lasted enough time to comment on it to my passenger! This time it was 100% definitely maintaining the throttle setting I'd given it when changing gear, which was enough to take it to about 5500 RPM with the clutch down, so a sorta 1/3rdish throttle setting. And then the ABS etc lights all go back on again.
Anyway I won't keep updating thread until it's been looked at. But it's very odd.
OK, that definitely sounds like a throttle actuator kind of problem. Just to outrule the obvious first - your carpet mat isn't leaning on the throttle pedal, or some other obstruction down there?
You haven't stated the age of the car, but I'm assuming it's new enough to be a DBW throttle? Otherwise I would suggest a sticking throttle cable.
Could be a bad air leak or idle control not kicking in when you back off the gas. I would get it to a specialist as it sounds pretty dangerous!
You haven't stated the age of the car, but I'm assuming it's new enough to be a DBW throttle? Otherwise I would suggest a sticking throttle cable.
Could be a bad air leak or idle control not kicking in when you back off the gas. I would get it to a specialist as it sounds pretty dangerous!
Although I the throttle makes sense in isolation I just can't understand why in every incident it would happen exactly once, only when the ABS/brake warnings are off, and immediately trigger them if it's a separate problem. But equally I can't see what ABS/DSC has to do with a throttle!
Somewhatfoolish said:
Although I the throttle makes sense in isolation I just can't understand why in every incident it would happen exactly once, only when the ABS/brake warnings are off, and immediately trigger them if it's a separate problem. But equally I can't see what ABS/DSC has to do with a throttle!
What, you don't understand why the DSC would want to control the throttle?How do you expect otherwise the DSC would cut power to the wheels when needed?
E-bmw said:
Somewhatfoolish said:
Although I the throttle makes sense in isolation I just can't understand why in every incident it would happen exactly once, only when the ABS/brake warnings are off, and immediately trigger them if it's a separate problem. But equally I can't see what ABS/DSC has to do with a throttle!
What, you don't understand why the DSC would want to control the throttle?How do you expect otherwise the DSC would cut power to the wheels when needed?
Somewhatfoolish said:
E-bmw said:
Somewhatfoolish said:
Although I the throttle makes sense in isolation I just can't understand why in every incident it would happen exactly once, only when the ABS/brake warnings are off, and immediately trigger them if it's a separate problem. But equally I can't see what ABS/DSC has to do with a throttle!
What, you don't understand why the DSC would want to control the throttle?How do you expect otherwise the DSC would cut power to the wheels when needed?
It is just an electronic part & they can go wrong in a multitude of ways.
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