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      11-20-2013, 10:00 PM   #1
TDIwyse
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425D Accelerator Pedal Potentiometer Plausibility

Well, my car lost all power late this afternoon. Fortunately it was only a couple miles from my house. The car only idles, and whenever I press the fuel pedal I get a large 1/2 colored engine symbol and a "bling", but no Service Engine Soon light.

It starts fine, idles fine, just can't raise rpm's. The Bavarian Technic tool shows code 425D, and looking online that BMW code relates to: Accelerator Pedal Potentiometer Plausibility.

I've checked all the fuses in the glove box, and all are good.

Anybody have any experience with this?
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      11-20-2013, 10:26 PM   #2
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Have you changed your pedals recently? Any engine tunes?
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      11-20-2013, 10:51 PM   #3
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Quote:
Originally Posted by GreekboyD View Post
Have you changed your pedals recently? Any engine tunes?
Pedal change = No.
Engine tune = Yes. And DPF was removed and re-installed and that involved a lot of tight reaching/wrenching ...

Are there other places for fuses besides the glove box area to check?

Anyone know how to test the accelerator module to see if it's working?

I'm hoping it's as easy to remove as this:

http://www.e90post.com/forums/showthread.php?t=471441
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      11-20-2013, 10:57 PM   #4
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Not sure about other fuses being elsewhere but the pedal is just as easy to remove like your link shows. Seen my buddy do it many times at his shop.
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      11-21-2013, 02:26 AM   #5
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I confirm. I have close to zero mechanical knowledge and I removed the pedal in 5 minutes. Extremely easy.
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      11-21-2013, 08:58 AM   #6
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Thanks, that's good to know.
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      11-21-2013, 05:56 PM   #7
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So ... turns out the accelerator pedal has two internal potentiometers which are used in the drive by wire system. The Bavarian Technic tool shows pot 1 going from ~0.4V to ~4.5V upon progressive pedal application, but pot 2 is staying at ~0.4V.

From the "BMW Vehicle Communication Software Manual"

https://www.google.com/url?sa=t&rct=...56988011,d.aWM

Page 40-41 of this document talks about the drive by wire systems and the different "accelerator pedals" and the double redundancy. We appear to have the two potentiometer system and one of mine is not responding to pedal application. This would make sense for the fault I'm seeing as the computer is expecting these two values to agree. Unfortunately, it makes the car completely non-drivable as the rpm's can not be raised above idle. Having my wife drive the big Cummins to tow me home on the back gravel roads last night was a fantastic red neck adventure ...

New pedal on order.

Also, the pedal was indeed extremely easy to remove from the vehicle.

Last edited by TDIwyse; 11-21-2013 at 09:39 PM. Reason: Left out "easy" in "...extremely easy to remove ..."
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      11-21-2013, 07:04 PM   #8
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Quote:
Originally Posted by TDIwyse View Post
So ... turns out the accelerator pedal has two internal potentiometers which are used in the drive by wire system. The Bavarian Technic tool shows pot 1 going from ~0.4V to ~4.5V upon progressive pedal application, but pot 2 is staying at ~0.4V.

From the "BMW Vehicle Communication Software Manual"

https://www.google.com/url?sa=t&rct=...56988011,d.aWM

Page 40-41 of this document talks about the drive by wire systems and the different "accelerator pedals" and the double redundancy. We appear to have the two potentiometer system and one of mine is not responding to pedal application. This would make sense for the fault I'm seeing as the computer is expecting these two values to agree. Unfortunately, it makes the car completely non-drivable as the rpm's can not be raised above idle. Having my wife drive the big Cummins to tow me home on the back gravel roads last night was a fantastic red neck adventure ...

New pedal on order.

Also, the pedal was indeed extremely to remove from the vehicle.
TDI, you had your leadfoot in it and wore out the pedal
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      11-21-2013, 07:20 PM   #9
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Odd that it made the car dead in the water if it was a redundancy system. Would have expected it to allow you to continue to drive but with a check engine light as long as one pot showed functional.
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      11-21-2013, 07:35 PM   #10
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Quote:
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TDI, you had your leadfoot in it and wore out the pedal
Nice.
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      11-21-2013, 07:40 PM   #11
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Quote:
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Odd that it made the car dead in the water if it was a redundancy system. Would have expected it to allow you to continue to drive but with a check engine light as long as one pot showed functional.
That's what I would've hoped for. Even a little rpm rise would've been enough to limp me home...

I didn't find any other 335d reports on this issue online from my searches, so I'm not sure what is "normal" for this type of fuel pedal issue. But I do not like this type of failure mode...
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      11-21-2013, 09:26 PM   #12
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Quote:
Originally Posted by Mark M
Odd that it made the car dead in the water if it was a redundancy system. Would have expected it to allow you to continue to drive but with a check engine light as long as one pot showed functional.
= no lawsuits
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      11-21-2013, 10:33 PM   #13
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Tdi, did you have any other related fault codes at the same time? If so, perhaps the software is coded to ignore the redundancy pot and just shut down in the event of multiple codes.
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      11-21-2013, 10:53 PM   #14
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Quote:
Originally Posted by Mark M View Post
Tdi, did you have any other related fault codes at the same time? If so, perhaps the software is coded to ignore the redundancy pot and just shut down in the event of multiple codes.
I did, because I had been monitoring/playing with the electronic EGR sensor. At first I thought the issue was related, but after clearing codes and restarting car all I get is the code related to the accelerator pedal and the signals/behavior of the EGR are similar to what I had been measuring previously. And the BT measured data shows pot 2 not responding as the pedal is pressed.

From that link above this is a description of how the two pots should relate to each other:

ME7.2 (E39, E38, E53)
The ME7.2 system does not use two Hall sensors for pedal position, but instead uses two potentiometers mounted in the PWG sensor housing at the driver's footwell. Also, ME7.2 does not use a separate idle control motor.
The pedal position sensors should read approximately the same for any throttle position:
Pedal position 1 (potentiometer 1): 0.54.5V
Pedal position 2 (potentiometer 2): 0.54.5V


Found some stuff about "failsafe" with one of the pots goes bad, but its all for the gas cars. In those cases there are some potential modes of operation where 1/2 power is allowed, or a max of ~1300rpm is allowed, or no rpm increase and rough idle happens. My 335d didn't exhibit any of these modes (idle was smooth as normal, but no rpm response)...
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      11-22-2013, 06:57 AM   #15
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wow thats a first i had drive by wire for my 02 MCS and Never went bad, your case is unique and Gracias for the input
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      11-22-2013, 02:40 PM   #16
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I have seen this before but on Mercedes, we have had big problems with sprinter vans doing this. It will lose one branch of the throttle pedal which will cause you to lose some feeling from the throttle, it will still rev but very slow! If you lose both or they contradict each other badly it will cut throttle! We have numerous failures over the last few months.
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      11-22-2013, 03:19 PM   #17
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I have seen this before but on Mercedes, we have had big problems with sprinter vans doing this. It will lose one branch of the throttle pedal which will cause you to lose some feeling from the throttle, it will still rev but very slow! If you lose both or they contradict each other badly it will cut throttle! We have numerous failures over the last few months.
that sounds like the case with TDI's pedal. If one branch was reading 0.5V at all pedal positions then the other circuit would be widely different any time the pedal moves.
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      11-22-2013, 04:57 PM   #18
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Interesting feedback Dan.

Hooper, any chance you could use your BT to check the accelerator pedal 1 and 2 voltages on your functioning vehicle as you push on the pedal to see what things should look like? I found them in the engine module down under the "Sensors" section. I'd be interested to see roughly how they match each other.

New pedal should arrive Monday.
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      11-22-2013, 11:28 PM   #19
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The values I'm seeing are about double each other. The base readings are .356v and .712v, peak reading is 2.077v and 4.125v. I did it with the engine off so I gave the dde plenty of time to settle before writing it down. I only found one reading for position readout as a %, which ranged from 0.0% to 100.1%
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      11-23-2013, 06:09 AM   #20
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Hooper your pedal does exactly like ours on the mercedes when they work correctly. All vehicles now use the same format for there throttle pedal!
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      11-23-2013, 07:50 AM   #21
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Quote:
Originally Posted by Hoooper View Post
The values I'm seeing are about double each other. The base readings are .356v and .712v, peak reading is 2.077v and 4.125v. I did it with the engine off so I gave the dde plenty of time to settle before writing it down. I only found one reading for position readout as a %, which ranged from 0.0% to 100.1%
Thanks for checking that.
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      11-25-2013, 11:50 AM   #22
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New pedal arrived and I put it in and ... it's drivable again. Hope this one lasts longer than ~3 yrs.
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