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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 10-29-2008, 01:33 PM   #1
JonHsiung
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Got an EML & ASC Light + Limp mode? Fix to the TPS sensor (+pics)

What happened:
I was driving home and while the car was decelerating following an acceleration, engine power cut out and went into limp mode. "ASC traction" light turns on (the exclamation mark with a triangle around it) as well as the "EML" light and "Check Engine" light. It seems that only about 20% engine power could be used.

I pulled over and restarted the car and after driving a few miles, the same thing happens again. Doing it again, it started occurring more frequently at which point I got home two stops later.

What you need:
  • OBD-II Scanner
This is a MUST-HAVE in most garages! The dealer will easily charge you double the cost of ONE of these just to read your codes once. The scanner also works in nearly any car made past 1996 since the system is largely universalized. If you're in SoCal, PM/email me if you need me to read your code.
http://www.amazon.com/Actron-CP9145-.../dp/B00020BM2S
  • Multimeter
Something that can be used in far more than car parts, I would highly recommend picking up one of these too. You can get them for pretty cheap online. They measure electricity flow and continuity on pretty much any application you can think of.
http://en.wikipedia.org/wiki/Multimeter
  • Philips head-bit, socket wrench set
  • Flathead screwdriver (not necessary)
  • Angled Pliars (not necessary)

Use the OBD-II scanner and PULL THE CODES. Without the proper codes, you won't know what's wrong with your car - it has sensors and diagnostic checks to make sure that it lets you know what the problem is. When I pulled the code, I got "P0121 TPS Sensor." What a TPS sensor is a Throttle Position Sensor which measures where the throttle is. I also got a few other TPS codes and a mixture issue, possibly caused by a number of reasons as the car stalled and such during this ordeal.

Background Information
To understand what is going on, the easiest way to do it is to picture it in your head. You have a three TPS sensors in the M3, because it's a fancy "drive-by-wire" system, there is no actual hard line that runs from your gas pedal to the engine as in most cars. It sends an electrical signal to the engine to tell it how much you are pushing down the pedal. A TPS sensor is mechanically something called a "potentiometer" which is a fancy way of saying a switch that tells you how much you are pushing it down. Read more about it here if interested:
http://en.wikipedia.org/wiki/Potentiometer

Because of this "drive-by-wire" system you have three potentiometers in your M3. One is your pedal, which has to measure how much you push the pedal to give off a signal. And the other two I am not sure about, but theoretically I assume one that measures how much the throttle body opens (the front one) that is hooked up to the throttle on the engine, and another one that is apparently behind the intake or something. Anyway, according to other threads, it's less common when that one goes out so we'll focus on the first two and if it doesn't fix your problem...you're boned, have a nice day.


Disassembly
It's pretty simple. For the front TPS sensor, you take your philips head bit and socket wrench to unscrew the two screws and pull the TPS directly toward the front of the vehicle. There's an O-ring and the circular aluminum covering also may pop off, so just keep your other hand under it when you pull it off.



For the gas pedal, from kneeling position you'll see a white tab and on the right side (against the firewall) that you can't see, there is a sensor and connection there. Disconnect that link by hand, but it also helps to have angled pliars. Then you push the white tab and pull the pedal sideways toward the brake pedal. It should slide right out.

Diagnosis
Now with most TPS sensors, they have a given range. I watched this video on YouTube and they say it should normally give a 0.5 ohm reading when you aren't pushing the gas pedal and 4.5 reading when it's floored.


Put your multimeter on 20-ohms and connect the two probes to two of the three pins until you get a reading (usually outer and middle). Measuring my FRONT TPS SENSOR I got 0.93-ohms and 5.56-ohms. If it moves COMPLETELY SMOOTHLY then it is NOT BROKEN. However, if there are spikes on the ohmmeter while you rotate the little white thing inside, then you can go to www.getbmwparts.com and overnight the sensor so you can get to work the following day (call your boss to let him know you're sick tomorrow). Mine was completely smooth, so I didn't have to bust $130 on this part - price according to other threads.

Next, was the gas pedal TPS sensor. There are six leads and to be honest, I don't remember which ones I used, but along the first row of three pins, try two of those and if it reads 0, try the other two. Same with the second row of pins. It helps if you have a steady hand and a friend to either hold the multimeter's probes or push the gas pedal down. Mine had a spike while pushing down the pedal. In fact, it was all over the place from 0-ohms to 4-ohms and all the way to 12-ohms or so. My gas pedal is f'd. I overnighted a new gas pedal from Tischer BMW and it came the next morning. Right under $160 shipped across the country. My local BMW dealerships wanted $175 + California tax (8.25%) and a 2-3 day wait since none of them had it in stock.


My old one was made in 02 and the new one in 08. Little difference except the new one is like an ounce lighter, can't stand by itself on a desk (weight is off?), and doesn't have the rubber bushing shown in the picture below.



Installation is easy and just reverses the way I took it out. With the new gas pedal, I've noticed the following results:
  • Better throttle response
    Less jerkiness (the car & me)
    Smoother shifts
    No engine-cutting out on the freeway when I pop it in neutral to roll down a big hill
    Easier getting into gear 1 and 2

My Theory
When I think about it, it kind of makes sense - when the potentiometer can't give a smooth signal, it sends a spike to the ECU and when throttle used to be at 20% going to 25% and suddenly spikes to 80% for a split second, the car freaks out. The engine usually follows along for a while, hence the jerkiness in my power delivery in the past. When enough of the TPS/potentiometer is messed up, it just sends garbage signals to the ECU and thus the ECU says "I'm not having any more of this ****" and puts you on limp mode and only gives you a little bit of power so you don't feel like you're driving a mechanical bull. Then it waits until you fix it.

Well, I hope this writeup helps somebody. It was a bit stressful of an ordeal, but through a diligent diagnosis and researching a bit about the situation, I probably saved myself $600 of labor at the dealership and a couple days of my life without a car.

Special thanks to the other people on this forum. I'll post quotes that I found helpful.
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Old 10-29-2008, 01:35 PM   #2
JonHsiung
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Special thanks to HiRide for his explanation:

Quote:
Originally Posted by HiRide View Post
what it means is that the EML light only comes on when you have a throttle related problem. What its saying is that if the EML light is on, you have a throttle pedal, or TPS, or throttle body problem that could be related to vacuum.

If you are in limp mode and the EML light comes on you most likely have a faulty TPS sensor. There are TWO tps sensors in the car.

One is the actual GAS PEDAL which is the most common failure. The other is the TPS sitting just over the oil filter attached to the throttle bodies.

It could also be the throttle body servo motor, but not likely at all. Also, do not let BMW tell you that you need to replace all the throttle bodies. Thats crap... the most you would have to do is get new servo motor and recalibrate the system.

Sounds like its the TPS or pedal though.

Also, the Cats had nothing to do with that EML... the only time you will replace cats is if you get a SES light with o2 sensor codes. Think about it... what are the only sensors that can tell you if the cats are working. O2 sensors, and they can only tell you whether the exhaust gas after the cats has too much fuel in it. The only way would be the cats being so clogged the exhaust could not even get through and you would have had check engine lights for months and the car running rich as hell for that to happen.... Even then, you should not get EML.

Also, you can completely remove the cats and run with the SES light and no limp mode... The dealership should have never even suggested cats. I dont understand how BMW can build a car, and then BMW does not know how its own diagnosis system works.... And yet everytime you go into the dealership they always look so confused when the SES or EML light comes on. No one ever knows what the EML light is for and it never stores codes that can be read through the OBD system.

I just dont get it... anyway, long story short. cats cant cause the problem. most likely TPS or pedal. It is actually pretty common, but no one ever posts their success on fixing the problem after they post up about the EML light.
Quote:
Originally Posted by HiRide View Post
thats a little high, and they are assuming it is the most difficult of the 3 TPS sensors right off the bat.

There are 3 TPS sensors on the S54. There is the one they mentioned to you which is the most expensive job, it does require removing the inlet manifold and while it is a larger job, it is not a $831 USD job...! That is crazy.

If you are not covered under warranty then you should no longer use BMW for anything. They charge over $120/hr labor here and they probably charge a similar amount in the UK.

There are two other sensors: One is located in the gas pedal and if it goes out, the entire gas pedal has to be replaced. This is the second most costly repair, but an easy one as its just a remove and replace procedure.

The cheapest TPS is the one located on the front end of the motor just above the oil filter housing. You actually have to unplug this TPS in order to change the oil. This is the cheapest and easiest TPS to replace.

I would go back to BMW and ask them if they are 100% sure that the job they want to do will fix the problem. They will most likely say no. You then ask about the other parts, the TPS sensor on the front of the motor and the gas pedal. They will most likely say that it could be those and they dont know exactly which one.

Try going to an independent BMW shop and get a diagnosis and quote from them. The sensor under the inlet manifold has been known to be the most likely culprit but its the most expensive job and not usually the one you want to try first if you dont have any concrete proof.

I would start with the TPS on the front of the motor... if that doesnt work, then i would consider going under the inlet manifold or replacing the gas pedal, but you take a gamble either way.

Good Luck!

Last edited by JonHsiung; 10-29-2008 at 01:40 PM.
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Old 10-30-2008, 12:54 AM   #3
cityjohn
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Thanks for the thorough explanation and pics. This exact situation happened to me, codes and everything.

Also, if you can't reach the phillips screws head on, DON'T do it at an angle. I tried to do this away from home using the BMW toolkit screwdriver. You can easily strip the screwhead like I did. Find a shorter driver or carefully remove the engine hoist bracket (wait til engine is cool -- it opens up the cooling system)
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Old 01-28-2010, 08:49 PM   #4
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excellent write up! i have learned a lot from this thread.
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Old 01-30-2010, 11:58 AM   #5
playskool1
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i checked REALOEM and both TPS sensors (near oil filter and under intake manifold) are the same part number??? i just wanted to double check before i order another one.
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Old 01-30-2010, 12:02 PM   #6
mredwin25
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Quote:
Originally Posted by playskool1 View Post
i checked REALOEM and both TPS sensors (near oil filter and under intake manifold) are the same part number??? i just wanted to double check before i order another one.
Yes they are the same
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Old 01-30-2010, 03:15 PM   #7
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Quote:
Originally Posted by mredwin25 View Post
Yes they are the same
thanks!!!!!!
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Old 05-19-2010, 10:23 AM   #8
kaansahbaz
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I'm trying to remove my gas pedal but need some help. Anybody got info?
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Old 05-19-2010, 11:01 AM   #9
JonHsiung
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Disconnect the wire, push down on the tabs while sliding the whole thing leftward. It's pretty stuck in there, but after you get it out you'll realize that you just needed to slide it leftward.
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Old 05-19-2010, 11:08 AM   #10
dirkramrod
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Just wanted to say thank you for this thread. I had this happen to my car (on a 3000km road trip) and while i didn't do the work myself, i was at least able to feel comfortable knowing this was the issue and not something more serious.

Thanks!
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Old 06-01-2010, 03:42 AM   #11
kevro
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Next, was the gas pedal TPS sensor. There are six leads and to be honest, I don't remember which ones I used, but along the first row of three pins, try two of those and if it reads 0, try the other two. Same with the second row of pins.

I was hoping to re-address this, I have tested my tps from the front of the motor and found it to be good.
The pedal has 6 pins kinda like this

. . .
. . .
1 2 3
if i connect pins 1 and 2 i get zero reading
if i connet pins 2 and 3 i get a reading of .48 ohms.
however it does not change at all when the gas pedal is pressed/depressed
I have two gas pedals and both of them respond the exact same way.

when checking pins on top row, assuming the same numbers, same thing on both pedals.

I really feel like I am doing it wrong. If there was no change at all, the car wouldn't have moved at all.
I assume when you tested you separated the top row from the bottom row? I have read there are actually two tps built into one sensor to give the cpu a better idea of actual readings vs bad readings?


the tps from the front of the motor tested EXACTLY as you described above and smoothly throughout the range.

Any help would be greatly appreciated
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Old 06-03-2010, 02:45 PM   #12
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Old 12-23-2012, 11:20 AM   #13
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Quote:
Originally Posted by kevro View Post

Next, was the gas pedal TPS sensor. There are six leads and to be honest, I don't remember which ones I used, but along the first row of three pins, try two of those and if it reads 0, try the other two. Same with the second row of pins.

I was hoping to re-address this, I have tested my tps from the front of the motor and found it to be good.
The pedal has 6 pins kinda like this

. . .
. . .
1 2 3
if i connect pins 1 and 2 i get zero reading
if i connet pins 2 and 3 i get a reading of .48 ohms.
however it does not change at all when the gas pedal is pressed/depressed
I have two gas pedals and both of them respond the exact same way.

when checking pins on top row, assuming the same numbers, same thing on both pedals.

I really feel like I am doing it wrong. If there was no change at all, the car wouldn't have moved at all.
I assume when you tested you separated the top row from the bottom row? I have read there are actually two tps built into one sensor to give the cpu a better idea of actual readings vs bad readings?


the tps from the front of the motor tested EXACTLY as you described above and smoothly throughout the range.

Any help would be greatly appreciated
I am having a similar issue. I have checked all combinations of pins and either get an open circuit, 461 omhs or 58 ohms. And as with kevro, when the pedal is pressed i get no change in resistance... Anyone else have better luck? Or is my pedal just junk?
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Old 01-18-2013, 02:04 AM   #14
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It looks like they use Hall sensors, not potentiometers.

These are a non contact mechanism using a magnet and a sensor that detect magnetic field. They offer high reliability.

See http://www.ge39.com/files/m54x5.pdf

Testing would need to be with the ignition in the run position using a volt meter.

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Old 08-10-2013, 11:45 AM   #15
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Sensor can be tested while REMOVED from vehicle

This thread was helpful to me, but it was apparent from reading that there is some confusion about how to test the throttle postion sensor, namely whether it should be done in the vehicle or with the device removed.

This morning I removed the sensor which is located immediately next to the oil filter cap. I can echo a previous poster's comments that you need to use proper tools here. The two phillips headed screws which attach the sensor are not hardened and unless you have a tool which properly fits the screw heads you run a serious risk of stripping them. I used a right angled socket set with a very short philips driver in it, but even with this I found that I couldn't put enough sideways pressure on the lower screw to avoid some obvious slipping of the driver. I stopped, pondered for a moment how to proceed and eventually found that a large crowbar with the flat end turned sideways gave me a perfect lever to wedge against the engine hoist loop (I think that's what it was anyway) and the backside of my socket driver. With alot of force pushing the driver into the head I was just barely able to break the screw loose and it started turning.

Enough of the warnings ;-) The purpose of my post is to make clear to future readers that this particular sensor is essentially a variable resistor and should be tested outside of the vehicle with a multimeter set to resistance readings. I found it tricky to get the multimeter clips attached to the sensor connector because the tabs are recessed. I ended up modifying some crimp-style electrical connectors which have male and female sides. I cut the female side in half and then was able to slip it over a tab and effectively extend it so that it was easy to attach. After doing this on both tabs (I used an outside and the center tab) and then putting a wide flathead screwdriver into the rotating socket, I was able to (unfortunately) observe resistance changing from about 1.1 ohms up to about 4.9 ohms ( approximately, I didn't write these down) with no glitches. Of course this test isn't perfect, but it convinced me sufficiently that this sensor is likely working as designed.

Now I'm off to search for how to locate the next most likely sensor, either the one on the pedal or the one under the intake manifold!
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Old 10-19-2010, 11:14 AM   #16
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part number for the TPS for reference
13-63-7-840-383
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Old 03-09-2011, 10:48 PM   #17
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Ive experienced the same problem and have changed the TPS sensor in the Engine bay and the entire pedal assembly and the problem still keeps occurring.... What should I change now?
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Old 07-03-2011, 10:58 AM   #18
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Quote:
Originally Posted by kevinm3 View Post
ive experienced the same problem and have changed the tps sensor in the engine bay and the entire pedal assembly and the problem still keeps occurring.... What should i change now?
this.
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Old 07-03-2011, 07:42 PM   #19
Rodney @ FinalTouchMotorsports.com
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If you get an error code for a TPS cross check - I usually see people miss diagnose the problem- to fix this you need to change the TPS sensor above oil housing and the TPS sensor on the electric throttle actuator - they are both the same part number- to change the second one you need to remove the intake manifold.

I own two of theses e46 m3's personally- They should really be changed arounf 50k especially in an SMG car- the drivability will improve so much it will feel like a new car too you.
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Old 07-12-2011, 08:30 PM   #20
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My ems light just came on today, same story...restart the car and it goes away, I ran the codes and it came up with a P2127 (Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage)

Is this talking about the TPS Sensor in the Pedal hence I should replace my pedal as well??
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