Scary unrequested full throttle - Merc
Discussion
My mom was driving my dad's nearly new Mercedes CLS350 at about 20mph and it suddenly shot forward at full throttle, it was all she could do to bring the car to a halt, engine still straining at the leash, she managed to get it switched off and restarted and parked up in a place of safety. the local Mercedes dealership recovered it and plugged a diagnostic reader into it. no errors shown so they say it is fine and wash their hands of it.
My mom has asked me to find out if there are many other instances of this sort of toyota-like behaviour from other mercedes, recalls etc. does anyone have any hints/tips to get mercedes to take them seriously because at the moment they are being told to just drive the car which they are understandably reluctant to do.
Mods- please don't move this to a merc specific backwater, i need a more generalist readership. Thanks
Greg
My mom has asked me to find out if there are many other instances of this sort of toyota-like behaviour from other mercedes, recalls etc. does anyone have any hints/tips to get mercedes to take them seriously because at the moment they are being told to just drive the car which they are understandably reluctant to do.
Mods- please don't move this to a merc specific backwater, i need a more generalist readership. Thanks
Greg
http://online.wsj.com/article/SB100014240527487038...
The current state of play is footmats or driver error.
The current state of play is footmats or driver error.
tstorm that Toyota had?For the DBW throttle to achieve eWOT without the pedal being in a position which requests maximum torque would be a very, very, very serious problem for Merc - the safety system in place on all DBW cars is massive and capable.
To give you a brief overview, there are two pedal position sensors and two throttle position sensors (to provide redundancy) which provide positional information on the throttle butterfly/flies and pedal position, the pedal essentialy works as a demand for torque and from the pedal position the engine controller can calculate a requested torque and shuffle various things (throttle position, cam phasing, boost pressure/supercharger engagement etc. etc.) about to achieve this torque request. To mitigate against stuck throttle butteflies, large inlet air leaks post throttle body etc. etc. the engine controller will look at RPM rise rate, mass air flow, vehicle speed, manifold pressure and a whole host of other things to determine if the engine is delivering the torque that the drive has requested e.g. if the pedal is requesting 15% of max torque but the engine speed is accelerating at rise rate X which is 30% higher than the allowed and expected rise rate of Y coupled with the MAF sensor showing an inducted air mass a percentage higher than expected for that required to produce 15% of max torque the engine controller will shut down the H-bridge which powers the throttle body and allow the return spring to bring the butterfly to a nearly closed position which allows around 2000RPM of engine speed unloaded. To mitigate against position sensor failures there is logic applied to the amount both TPS and both PPS sensors can disagree by, if a PPS or TPS sensors fails the engine controller will enter reduced performance mode, allow a minimal amount of throttle opening (to "get you home") and illuminate a number of MIL lights. In addition on some systems there is additional hardware within the engine controller which 'votes' on the decisions the controller is making and if they are valid, if the votes don't match the throttle H-bridge/bridges is/are shut down. Any issue, any where in the DBW/ETC system is logged.
In short it's extremely difficult for the DBW throttle system to make a mistake with regards throttle butterfly position and DBW/ETC is actualy extremely safe and far less prone to providing unrequested throttle openings than a conventional cable system is. The one thing it can't spot though is a floor mat or similar jamming the pedal.
I'm not sure what pedal position sensor setup the car in question uses but at one point Merc used a cable driven PPS (just to add an additional failure point!), if the cable sticks or something physicaly stops the PPS sensor returning then the ECU will see this as a valid torque demand.
To give you a brief overview, there are two pedal position sensors and two throttle position sensors (to provide redundancy) which provide positional information on the throttle butterfly/flies and pedal position, the pedal essentialy works as a demand for torque and from the pedal position the engine controller can calculate a requested torque and shuffle various things (throttle position, cam phasing, boost pressure/supercharger engagement etc. etc.) about to achieve this torque request. To mitigate against stuck throttle butteflies, large inlet air leaks post throttle body etc. etc. the engine controller will look at RPM rise rate, mass air flow, vehicle speed, manifold pressure and a whole host of other things to determine if the engine is delivering the torque that the drive has requested e.g. if the pedal is requesting 15% of max torque but the engine speed is accelerating at rise rate X which is 30% higher than the allowed and expected rise rate of Y coupled with the MAF sensor showing an inducted air mass a percentage higher than expected for that required to produce 15% of max torque the engine controller will shut down the H-bridge which powers the throttle body and allow the return spring to bring the butterfly to a nearly closed position which allows around 2000RPM of engine speed unloaded. To mitigate against position sensor failures there is logic applied to the amount both TPS and both PPS sensors can disagree by, if a PPS or TPS sensors fails the engine controller will enter reduced performance mode, allow a minimal amount of throttle opening (to "get you home") and illuminate a number of MIL lights. In addition on some systems there is additional hardware within the engine controller which 'votes' on the decisions the controller is making and if they are valid, if the votes don't match the throttle H-bridge/bridges is/are shut down. Any issue, any where in the DBW/ETC system is logged.
In short it's extremely difficult for the DBW throttle system to make a mistake with regards throttle butterfly position and DBW/ETC is actualy extremely safe and far less prone to providing unrequested throttle openings than a conventional cable system is. The one thing it can't spot though is a floor mat or similar jamming the pedal.
I'm not sure what pedal position sensor setup the car in question uses but at one point Merc used a cable driven PPS (just to add an additional failure point!), if the cable sticks or something physicaly stops the PPS sensor returning then the ECU will see this as a valid torque demand.
Matt Harper said:
Your Mom?
Presumably someone from Yankshire living over here....Use of the word Mom would lead the reader to believe/assume the author is of school age (circa 12 years old) , therefore the OP may not be taken seriously
Edited by bigdods on Saturday 13th November 01:01
bigdods said:
Matt Harper said:
Your Mom?
Presumably someone from Yankshire living over here....Use of the word Mom would lead the reader to believe/assume the author is of school age (circa 12 years old) , therefore the OP may not be taken seriously
Edited by bigdods on Saturday 13th November 01:01
Is it a diesel??
If it is, it can sometimes begin to run on engine oil, if for example the car is on a hill.
Has an oil change been done recently?
other than that, I'm sorry to say I also suspect user-error!
Perhaps you could try driving in the same manor (at the same place if inclines etc are involved!
If it is, it can sometimes begin to run on engine oil, if for example the car is on a hill.
Has an oil change been done recently?
other than that, I'm sorry to say I also suspect user-error!
Perhaps you could try driving in the same manor (at the same place if inclines etc are involved!
thanks for the replies thus far, i didn't realise that calling my mother mom was contentious, anyway....
tdfpeltd's reply is reassuring from a technical viewpoint, so assuming that merc have all of that good stuff on the car what precisely would have to fail to get the described action, basically everything or could the ecu having a brain fart be a (admittedly highly unlikely) outside possibility
as for big dods, you plum, go and pick an argument somewhere else
Greg
tdfpeltd's reply is reassuring from a technical viewpoint, so assuming that merc have all of that good stuff on the car what precisely would have to fail to get the described action, basically everything or could the ecu having a brain fart be a (admittedly highly unlikely) outside possibility
as for big dods, you plum, go and pick an argument somewhere else
Greg
Greg_D said:
thanks for the replies thus far, i didn't realise that calling my mother mom was contentious, anyway....
tdfpeltd's reply is reassuring from a technical viewpoint, so assuming that merc have all of that good stuff on the car what precisely would have to fail to get the described action, basically everything or could the ecu having a brain fart be a (admittedly highly unlikely) outside possibility
as for big dods, you plum, go and pick an argument somewhere else
Greg
For the car to suddenly accelerate without no input from the loud pedal would require either a mechanical failure/interference of the pedal/actuator like some can, floormat or the like being pushed in or the ECU failing unsafe.tdfpeltd's reply is reassuring from a technical viewpoint, so assuming that merc have all of that good stuff on the car what precisely would have to fail to get the described action, basically everything or could the ecu having a brain fart be a (admittedly highly unlikely) outside possibility
as for big dods, you plum, go and pick an argument somewhere else
Greg
ECU caused is extremely unlikely, particularly with no error flags.
Throttle jamming more likely, but the evidence should be there.
Most likely is user error, pressing the wrong pedal.
Probably nothing, but read the responses on here:
http://usnews.rankingsandreviews.com/cars-trucks/d...
Most seem to be referring to mercedes?!?
Even if it a known issue by them, they will not accept responsibility at all due to the possible media issues.
Could you try to recreate it yourself?
Also if it happens again get an Indy garage to read the error codes just in case
http://usnews.rankingsandreviews.com/cars-trucks/d...
Most seem to be referring to mercedes?!?
Even if it a known issue by them, they will not accept responsibility at all due to the possible media issues.
Could you try to recreate it yourself?
Also if it happens again get an Indy garage to read the error codes just in case
i have just fed your comments back to my parents and they find them curious because she was driving along just using the accelerator at 20mph in an urban environment when the car shot off, before this happened she wasn't using the brake so it isn't a case of fat feet, she only used the brake when the car accelerated. it wasn't slight acceleration either, it was flat out
Greg_D said:
i have just fed your comments back to my parents and they find them curious because she was driving along just using the accelerator at 20mph in an urban environment when the car shot off, before this happened she wasn't using the brake so it isn't a case of fat feet, she only used the brake when the car accelerated. it wasn't slight acceleration either, it was flat out
I'd have guessed she hit 'resume' on the cruise control but that should have cancelled as soon as she hit the brake...
, did myself one time going for the indicator, fGreg_D said:
i have just fed your comments back to my parents and they find them curious because she was driving along just using the accelerator at 20mph in an urban environment when the car shot off, before this happened she wasn't using the brake so it isn't a case of fat feet, she only used the brake when the car accelerated. it wasn't slight acceleration either, it was flat out
I'm sure all the Toyota drivers who thought it was the car (and the Audi drivers in the US in the 1980s) were equally adamant that it was not driver error.With respect, you passing on second hand comments is unlikely to get to the bottom of it, but there's a good body of evidence that driver error or a physical influence (such as floormats) causes this.
Edited by Jobbo on Saturday 13th November 10:57
TDFPELTD said:
To give you a brief overview, there are two pedal position sensors and two throttle position sensors (to provide redundancy) which provide positional information on the throttle butterfly/flies and pedal position, the pedal essentialy works as a demand for torque and from the pedal position the engine controller can calculate a requested torque and shuffle various things (throttle position, cam phasing, boost pressure/supercharger engagement etc. etc.) about to achieve this torque request. To mitigate against stuck throttle butteflies, large inlet air leaks post throttle body etc. etc. the engine controller will look at RPM rise rate, mass air flow, vehicle speed, manifold pressure and a whole host of other things to determine if the engine is delivering the torque that the drive has requested.
That's a great description! Thanks.The accidental engagement of "cruise" is a good suggestion. Given myself a surprise with that one -though it shuts down the moment you touch the brake pedal (with the brake light switch?) so not a big deal.
Some cars switch off the cruise control when the ignition key is removed and some don't. I'd have thought the Merc was likely to go fully "off".
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