BMW - Automatic gearbox over-rev?!
Discussion
Hi Guys,
I have a diesel BMW with "Sports" automatic, and I was going down a slight incline, and I downshifted - it went into 1st into first and it over-revved to the extent that it went off the rev-meter! - which was a huge surprise to me as it should prevent you from dropping a gear if its unsafe! I quickly pressed the "up" paddle within a couple of seconds which put me back into 2nd (including my reaction time to this strange case!) - the computer should not have let this happen.
As it went off the scale of the rev-meter, I couldn't really give a figure as to what it went to. Assuming that it continued a linear path, it would have been around 6,500rpm to 7,000 rpm. In 2nd gear it was around 3,500rpm approximately.
I cannot notice any difference with my car, and no engine or warning lights are on. However, is there anything I can check as a precaution? Or is it unlikely that any damage has been done?
Any advice would be fantastic!
EDIT: BMW found no faults logged with the car, not even an over-rev. I spoke to the technician (who seemed a nice chap) and he confirmed this again verbally. All he said is that if it happens again (which I sincerely hope it does not!!) they will send the diagnostic readings to BMW who may be able to read some error codes that they cannot in the dealership workshop. Furthermore, he added that there is no log of a similar fault/scenario in some central BMW fault-finding system they have.
I have a diesel BMW with "Sports" automatic, and I was going down a slight incline, and I downshifted - it went into 1st into first and it over-revved to the extent that it went off the rev-meter! - which was a huge surprise to me as it should prevent you from dropping a gear if its unsafe! I quickly pressed the "up" paddle within a couple of seconds which put me back into 2nd (including my reaction time to this strange case!) - the computer should not have let this happen.
As it went off the scale of the rev-meter, I couldn't really give a figure as to what it went to. Assuming that it continued a linear path, it would have been around 6,500rpm to 7,000 rpm. In 2nd gear it was around 3,500rpm approximately.
I cannot notice any difference with my car, and no engine or warning lights are on. However, is there anything I can check as a precaution? Or is it unlikely that any damage has been done?
Any advice would be fantastic!
EDIT: BMW found no faults logged with the car, not even an over-rev. I spoke to the technician (who seemed a nice chap) and he confirmed this again verbally. All he said is that if it happens again (which I sincerely hope it does not!!) they will send the diagnostic readings to BMW who may be able to read some error codes that they cannot in the dealership workshop. Furthermore, he added that there is no log of a similar fault/scenario in some central BMW fault-finding system they have.
Edited by sunnydude959 on Thursday 3rd October 21:45
Okay, thanks guys! - Does the over-rev get recorded in the ECU? I'm thinking of reporting it to BMW (dealership service centre) as the auto 'box shouldn't really have done it. I mean if it was a manual, I'd keep my lips sealed, but as the gearbox computer allowed it when it shouldn't have...
sunnydude959 said:
Okay, thanks guys! - Does the over-rev get recorded in the ECU? I'm thinking of reporting it to BMW (dealership service centre) as the auto 'box shouldn't really have done it. I mean if it was a manual, I'd keep my lips sealed, but as the gearbox computer allowed it when it shouldn't have...
It sounds more like your fault than that of the computer.If the car is within warranty get it to a dealer for a (free) looksee! No way should the transmission allow a downshift to an over rev condition, and yes max rpm will have been logged in both engine and transmission controller.
However, i doubt you managed to actually get to 7000rpm on a diesel, i would have expected the cam chain (or even crank!) to fail before than point due to the sudden crank accleration.
I'd do a quick check myself, put car i manual mode, find an empty road, drive up to say 4000rpm in second, and pull for a downshift, and see if it allows it again.
However, i doubt you managed to actually get to 7000rpm on a diesel, i would have expected the cam chain (or even crank!) to fail before than point due to the sudden crank accleration.
I'd do a quick check myself, put car i manual mode, find an empty road, drive up to say 4000rpm in second, and pull for a downshift, and see if it allows it again.
The transmission should never have allowed you to do that, your transmission control unit may be faulty or sensors that it relies upon are not working. A full diagnostic should sort this out.
The engine braking on a diesel is pretty harsh, it would have slowed itself considerably before much (if any) damage would have been caused. I once accidentally went into 2nd instead of 4th on a Hyundai Getz and it hit over 9k, no damage done though, and it carried on working happily for years
The main concern is why it would have allowed a downshift that would have moved it past an acceptable range
The engine braking on a diesel is pretty harsh, it would have slowed itself considerably before much (if any) damage would have been caused. I once accidentally went into 2nd instead of 4th on a Hyundai Getz and it hit over 9k, no damage done though, and it carried on working happily for years
The main concern is why it would have allowed a downshift that would have moved it past an acceptable range
hedges88 said:
The transmission should never have allowed you to do that, your transmission control unit may be faulty or sensors that it relies upon are not working. A full diagnostic should sort this out.
The engine braking on a diesel is pretty harsh, it would have slowed itself considerably before much (if any) damage would have been caused. I once accidentally went into 2nd instead of 4th on a Hyundai Getz and it hit over 9k, no damage done though, and it carried on working happily for years
The main concern is why it would have allowed a downshift that would have moved it past an acceptable range
I see two other possibilities. First the Transmission worked as designed, and kept the engine at below danger levels, though above normal levels, and secondly allowed an extra downshift even if it was potentially harmful. Some transmissions allow this, some AMG boxes for example. Possibly the BMW sport transmissions does, I've no idea.The engine braking on a diesel is pretty harsh, it would have slowed itself considerably before much (if any) damage would have been caused. I once accidentally went into 2nd instead of 4th on a Hyundai Getz and it hit over 9k, no damage done though, and it carried on working happily for years
The main concern is why it would have allowed a downshift that would have moved it past an acceptable range
Disco You said:
sunnydude959 said:
Okay, thanks guys! - Does the over-rev get recorded in the ECU? I'm thinking of reporting it to BMW (dealership service centre) as the auto 'box shouldn't really have done it. I mean if it was a manual, I'd keep my lips sealed, but as the gearbox computer allowed it when it shouldn't have...
It sounds more like your fault than that of the computer.eldar said:
I see two other possibilities. First the Transmission worked as designed, and kept the engine at below danger levels, though above normal levels, and secondly allowed an extra downshift even if it was potentially harmful. Some transmissions allow this, some AMG boxes for example. Possibly the BMW sport transmissions does, I've no idea.
Some AMG auto's allow the driver to exceed the engines rev limiter???The only thing I have ever known some Auto's to do in sports cars is not shift automatically at the redline, so that the car may be kept at/near the limiter
I have never seen an example of an auto box that will allow the driver to cause any damage to the drivetrain even on the most ancient automatics
If the weight of the car was pushing heavily down a hill it is possible that at the instant you called for the shift it was "just permissible" but by the time it took place the car had accelerated further.
It is also possible that the speed at which the revcounter needle swung round the dial it had enough momentum to fly past the true rev reading.
The transmission is to make the car "go". The brakes are to make it "stop" - and are much, much cheaper.
It is also possible that the speed at which the revcounter needle swung round the dial it had enough momentum to fly past the true rev reading.
The transmission is to make the car "go". The brakes are to make it "stop" - and are much, much cheaper.
I just saw that I wrote "hill" originally - it was more of a soft downward incline than a hill (i have edited the original post to reflect this).
I'm sure BMW would be able to tell me what rev's the car was actually doing, and if, as said above, the needle had enough momentum to keep going.
I'm sure BMW would be able to tell me what rev's the car was actually doing, and if, as said above, the needle had enough momentum to keep going.
hedges88 said:
Some AMG auto's allow the driver to exceed the engines rev limiter???
The only thing I have ever known some Auto's to do in sports cars is not shift automatically at the redline, so that the car may be kept at/near the limiter
I have never seen an example of an auto box that will allow the driver to cause any damage to the drivetrain even on the most ancient automatics
So I understand on the basis is the driver knows what gear to select, in either a manual or automatic. Something to do with launch control, I think.The only thing I have ever known some Auto's to do in sports cars is not shift automatically at the redline, so that the car may be kept at/near the limiter
I have never seen an example of an auto box that will allow the driver to cause any damage to the drivetrain even on the most ancient automatics
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