*SOLVED* Gas Pedal Issue - Consistent Potentiometer 2 Fault

[Darbshaw]

I originally posted this in the dumb question hoping it would be a quick fix, but unfortunately that is not the case.

Problem: I've been getting a sporadic limp mode and pedal position sensor 2 error code. I bought a low mileage replacement and was still having the issue on my car. Although this is where I've found it to be very inconsistent. Sometimes the error and limp mode trigger on immediate power on, other times I've gotten long stretches of time without the error occurring. In the end the code always appears on position sensor 2.

112

70

YES

Pedal-position sensor, comparison fault

06

B5

08

09

I've been using the DS2 program to read the live values from the pedal. Because I can see there's a consistent problem within the pedal reading, I'm not convinced this could be related to the TPS although if someone that knows more can share how I'm open to learning. At $200/sensor I don't necessarily want to replace it right away

Live Values:
Pedal 1: Stays mostly at 0% with a random variation of 0.2-0.4% without any input
Pedal 2: Has a lot more variability in readings when its supposed to be at 0%. Ranges jump anywhere from 0-1.5% when cold, and then as the car sits longer and warms up this variability jumps all the way from 0-4%

I took some video today of the variability, I'll edit this back in once I put it all together. Every pedal tested always ends up with a wide range at 0 input, and eventually throws a limp mode + 112 for a potentiometer 2 error

Pedal Wiring Diagram

Attempted Rememdies:
New Plug, the OG on the car was partially broken
2 Ebay verified working pedals
1 local junk yard pedal
1 pedal off my F82 (known working)
Physically inspected the wires up to the firewall with no visible signs of damage
Pins 1,2 have continuity with ground to the chassis
Pins 3,5 have confirmed voltage
Pins 6,4 checked continuity to X60004 pins 13,8


I did do the "lazy" way of trimming the wiring harness 3 years ago since this is a gutted track car. So there's a high chance of electrical gremlins, although I've ran 3 seasons since I trimmed the wiring out and haven't had an issue until this year. Last thing I changed electrically was making a jumper wire from my passenger tail light brake signal to the driver side, because in my trimming I accidentally snipped the driver brake switch signal. I don't think these are related but I'd love to be wrong.

If it matters, my car is an SMG swapped to 5 speed

Plan of attack to attempt next:

1. I have a spare ECU, so I'm pulling the tune off my current 54HP and then will transfer to the spare ECU. This should be able to rule out ECU issues.
2. Switch the signal wiring between sensors 1 & 2 to see if the variability follows the cable
3. Run new signal wiring between the pedal and ECU. Ground and voltage supply seems correct, but if you all think its better to run completely new wiring for the pedal I can always make this the hail mary

Thanks for any input on this. I'm lost at this point, electrical is not an area of comfortability.

[Darbshaw]

Alright well I managed to brick the spare ECU flashing it like an idiot. So this is off the table until I can find my bench test equipment.

I tried swapping signal cable wires but the ECU can't be tricked by this. It just causes hard errors and locks the pedal out.

What's left now is running a new wire for the signal.

I did manage to get a decent amount of run time (about 45 min) before a potentiometer 1 error on the eBay pedal. Good news is that it's potentiometer 1 and not 2 so something new.

DS2 points the error suggestion to bad voltage supply or signal. Although both pins are confirmed 5V and retested grounds today.


Sent from my iPhone using Tapatalk

[Darbshaw]

Done for the day, I consistently used the junkyard pedal and pulled some logs off of it. Attached is the error logs after the idle session with occasional blips and then the immediate key cycle, From running, pos 0, pos 2. You can see the data log here, can anyone confirm with DS2 on a running car if they have this much variability in pedal 2? No change came from testing today. I ran a new temporary wire using alligator clips and old plugs for the 5V & Signal wire for sensor 2 in the pedal. First session was just signal wire and second was signal and voltage. Signal only eventually threw a limp mode code. While signal and voltage seemed fairly resistant to the error and only threw the code after a few key cycles and throttle blips. Right now the most cost effective option is running new wiring, so I ordered new 22awg to replace this. Rock auto also had URO TPS for a fair price compared to FCP's BMW only. If anything these should provide a solid & new value compared to the worn ones on the car.

[sapote]

"Switch the signal wiring between sensors 1 & 2 to see if the variability follows the cable"
This won't work as the DME expect to see the positive slope for S1 and negative slope for s2. DME will be so mad at the swapped data vs what it expected.

"Pins 1,2 have continuity with ground to the chassis
Pins 3,5 have confirmed voltage
Pins 6,4 checked continuity to X60004 pins 13,8"
check for continuity is not enough for these sensitive analog signals: they are potentiometers with applied 5v rail and the signals will be converted by ADC in the DME. You need to measure voltage on all the pins on the sensors with engine running and write down the min and max with pedal locked to idle and other positions. The idea is to find which pin has the most variation of voltage which tell us it has a bad contact of the connection. I don't think the error related to TPS.

Either the bad data source at the pedal sensors, or it's good with stable data but you have a bad connection at the DME pin13 or pin8 (I don't know which is S1 or S2). If the wires from pedal to DME P13 and P8 are good with zero ohm resistance, then open the DME cover and measure voltage directly on the pcb side of p13 and p8 which should have the same data as at the sensor side, with engine on or running.

from the log it's clearly sensor 2 has the gross error of values jumping around badly [1.7 to 0] instead of a stable 1.7

[sapote]

Pedal Wiring Diagram

Be careful of using the wiring diagram, as the linked diagram is for MS43 and not our car. In this case they might be the same but other circuits could be much different.

[Darbshaw]

"Switch the signal wiring between sensors 1 & 2 to see if the variability follows the cable"
This won't work as the DME expect to see the positive slope for S1 and negative slope for s2. DME will be so mad at the swapped data vs what it expected.

"Pins 1,2 have continuity with ground to the chassis
Pins 3,5 have confirmed voltage
Pins 6,4 checked continuity to X60004 pins 13,8"
check for continuity is not enough for these sensitive analog signals: they are potentiometers with applied 5v rail and the signals will be converted by ADC in the DME. You need to measure voltage on all the pins on the sensors with engine running and write down the min and max with pedal locked to idle and other positions. The idea is to find which pin has the most variation of voltage which tell us it has a bad contact of the connection. I don't think the error related to TPS.

Either the bad data source at the pedal sensors, or it's good with stable data but you have a bad connection at the DME pin13 or pin8 (I don't know which is S1 or S2). If the wires from pedal to DME P13 and P8 are good with zero ohm resistance, then open the DME cover and measure voltage directly on the pcb side of p13 and p8 which should have the same data as at the sensor side, with engine on or running.

from the log it's clearly sensor 2 has the gross error of values jumping around badly [1.7 to 0] instead of a stable 1.7

Sapote, thanks for the additional info here on my problem, electrical is very outside of my expertise, but I'm willing/wanting to learn.

In my searching I did get very low resistance on pin 13 (I believe this is pedal 2), it was near similar to the resistance provided by a straight jumper wire for the pins. I understand it should be 0, but I figure an equivalent to my fresh wire ran could be put to my tools margin of error. Thanks for the catch on the wiring diagram. I did reference the proper one when doing my pin hunting to test the pedal & jumper wires.


My issue ended up being a dying DME. I'm not sure exactly what the cause was here, but I was able to save my spare DME thanks to DS2 and completed my track day with 0 issues. I'm not sure what caused the failure although I'm hoping to repair the failing one given the price of S54HP DME's left on the market. I was waiting to finish my track day this weekend after getting a full test session to report back.

[sapote]

My issue ended up being a dying DME. I'm not sure exactly what the cause was here, but I was able to save my spare DME thanks to DS2 and completed my track day with 0 issues. I'm not sure what caused the failure although I'm hoping to repair the failing one given the price of S54HP DME's left on the market. I was waiting to finish my track day this weekend after getting a full test session to report back.

Too bad you didn't have the chance to measure the voltages as I suggested: " You need to measure voltage on all the pins on the sensors with engine running and write down the min and max with pedal locked to idle and other positions. The idea is to find which pin has the most variation of voltage which tell us it has a bad contact of the connection. "

Maybe it's simple as the DME supplied a noisy 5v to the pedal sensor, which would cause jumpy data as on the log.