2002 E39 ASC BRAKE ABS lights on => Diagnostic Procedure & Parts Location

agent15 · Sep 12, 2010

I understand what you're saying, but you've not clarified how the dealer's scanning tool, whatever make and model it is, said that the LR sensor was the one throwing the fault code. I would imagine there is a difference between a scanner pointing to a particular wheel's sensor as "open," as in a wiring issue or a failed sensor itself, versus the sensor telling the car's OBD system that it has an issue while still maintaining continuity to it.

540iman · Sep 13, 2010

agent15 said:
I understand what you're saying, but you've not clarified how the dealer's scanning tool, whatever make and model it is, said that the LR sensor was the one throwing the fault code. I would imagine there is a difference between a scanner pointing to a particular wheel's sensor as "open," as in a wiring issue or a failed sensor itself, versus the sensor telling the car's OBD system that it has an issue while still maintaining continuity to it.

I think you are saying that you understand, but are dismissing the thought process. The dealer's scan tool, Carsoft, or whatever scanners see many different symptoms that they don't like. Missing pulses, no pulses whatsoever, misshapen pulses as viewed on an oscilloscope, etc. They know what portion of the module they reside in. They can't tell the mechanic the cause, only the symptom. So, they identify the portion of the module that is whacked AT THAT MOMENT IN TIME. If the car were on a dyno and the wheels spinning, it would be better, but still not absolute because then it would possibly know if it is seeing pulses that the wiring is ok, but the sensor itself LIKELY bad. My Carsoft told me on my realtor's car that his sensor wiring was at fault when he actually had a bad sensor itself. I have no clue how it thought it could be so specific as to identify the wiring and not the sensor, but that is what it said. The same software, on my car, said it was the sensor itself-and it was after I confirmed by disconnecting and checking sensor with the VOM.

I am not discounting that the scanners can diagnose some faults (like communication faults) 100%. They can properly identify defective modules in many cases-say when a module is pulling no current whatsoever. Only the module can cause a symptom such as this. When it gets to the speed sensors themselves, they can be right still, but at a smaller percentage because of the nature of how the sensors generally fail. MOST (not all) go open. The cheaper scanners such as Carsoft assume the module itself works as long as it has communication. If a channel is dead, it will always diagnose as a bad sensor or sensor wiring. It will not return a bad I/O transistor in the module correctly. It will not diagnose a bad solder connection in the module as such. It will deliver a bad sensor message 100% unless the solder connection is not in the speed sensor signal path (again, like a communication error caused by a bad solder connection)-that it will get right. Talk to your Stealership tech. and they will tell you. Mark (aka EAC tuning Mark) has software very similar to what the stealer has and while he is working many of the bugs out of it, he will tell you that there is a big difference between accurately diagnosing the symptom and the actual cause. That can be trial and error. Many here will tell you of countless sensors diagnosed and replaced on to ultimately find it is the module itself.

I don't know if I clarified for you to your satisfaction. I can only tell you what is and why I as an electronic tech can justify it. Just do not believe that all bad sensor diagnosis are correct. People have spent countless dollars chasing supposedly bad sensors read by GT-1s down to Peakes.

agent15 · Sep 13, 2010

540iman said:
The dealer's scan tool... can't tell the mechanic the cause, only the symptom. So, they identify the portion of the module that is whacked AT THAT MOMENT IN TIME.

I am not a mechanic, I do not have any first hand experience with using any of these particular pieces of hardware or software, and I am certainly not trying to discount your experience or knowledge on this subject. I can only regurgitate what I was told by the dealer who performed the PPI, which is there was a history of a fault code at the LR wheel sensor.

The PO told me the light trifecta issue had happened to him "two or three times and that it cleared itself the next time the car was turned on." The issue did not occur on my test drive of the vehicle, at the dealership during the PPI, nor at any time during the three hour drive home three days later when we exchanged money for keys. It did happen to me a couple of days later, and just as the PO said, cycling the ignition cleared the lights.

All that said, I definitely feel fortunate that I was able resolve the issue, at least temporarily, by a ten minute procedure at zero cost. I have asked the service manager at the dealership to send me the list of actual codes pulled during the PPI, since they're not doing either of us any good sitting in his files when we're geographically separated by two hundred miles. I will be happy to share them once they're in my hands.

540iman · Sep 13, 2010

Code "history" certainly helps. If I were a scan tool "expert" I would be building and selling them myself! Good mechanics and good technicians are a lot like Doctors in that they use many pieces of "symptom" to assign a cause. For example, shorts or opens can be intermittent, but generally do not display "heat-related" tendencies unless they may involve solder or very precise wire movement. When I hear of codes coming and going (clearing by themselves and then re-curring) MY experience points to a module. The sensor usually are good or bad. This includes metal shavings on sensor. Metal stays there until removed. Time driving relative to heat can be different than type of driving-stop and go creates more heat than 3 hour drive say on freeway. History of LR sensor errors that clear usually points to bad module with lose solder connection on module board at LR channel. History is your friend!

bluebee · Sep 13, 2010

I should repeat that scan tools told me three different (bogus it turns out) faults (previously mentioned in this thread).

I don't remember the actual BMW codes thrown (it's in the aforementioned thread), I think it was 41 and 81 but I'd have to check. One was the hydraulic pressure sensor, another was the wheel sensor, and another (which failed me for my smog even though it was bogus) was the official-sounding "P0500 wheel speed sensor") ...

NONE of those three bogus faults was "real".

By real I mean the sensor itself was fine. The problem, as Bill says, all along is that the diagnostic tool was, in effect, telling me the symptoms - but not the fault.

It should be enough to note that rebuilding the ABS control module cured all the faults (I had to manually clear the P0500 but it never came back). It has been about 9 months since this so I think Bill's explanation has stood the test of time, at least with me.

bluebee · Sep 13, 2010

agent15 said:
...history of a fault code at the LR wheel sensor.

Hi Agent15,
If this were my bimmer, and if someone told me I had a "history of a fault code" in my LR sensor, the FIRST thing I would do is open the hood and put my DMM leads on pin 13 and on pin 29. If the readings were bad (see chart below), I'd check the sensor at the wheel. If the readings are still bad, I'd replace the sensor. (Notice there's no need for fancy schmancy test tools.)

Now, if the readings were good, then I'd be in a quandary (presumably like you are in now). It could be my sensor was intermittent, or it could be the ABS control module is intermittent.

The "history" here is that almost everyone has an ABS control module that is intermittent to varying degrees before the trifecta stays permanently. There is NOT a reliable history of sensors being intermittent (AFAIK).

That combined history from multiple vehicles would tell me a lot.

agent15 said:
The PO told me the light trifecta issue had happened to him "two or three times and that it cleared itself the next time the car was turned on."

Same thing happened to me (if you look in post #48 you'll see I had one light, then two, then three, and it would, at first, go away when I restarted the car). This happens to a LOT of people.

So far, the intermittent and disappearing trifecta has happened to very many people here, most who have reported that the solution was to repair the ABS control module (many people don't report the solution so you have to throw out that data).

agent15 said:
The issue did not occur on my test drive of the vehicle, at the dealership

It's intermittent.

agent15 said:
It did happen to me a couple of days later, and just as the PO said, cycling the ignition cleared the lights.

It's intermittent. And it's (originally) cleared by cycling the ignition.

agent15 said:
I definitely feel fortunate that I was able resolve the issue, at least temporarily, by a ten minute procedure at zero cost.

My intuition tells me you'll get the trifecta soon enough again but I hope, for your sake, that the solution is permanent. I do realize the anguish of not being able to definitely ascertain the fault location when the ABS control module is concerned. As I've said many times, that's why it took me nearly a year to finally bite the bullet and "throw parts" at the problem by having my ABS control module rebuilt by ATE for $150 (includes shipping costs).

BTW, when you DO get the intermitent trifecta, are the speedo and odo and tripmeter adversely affected?

agent15 · Sep 13, 2010

It sounds like both of you are trying to tell me I'm wrong, albeit politely. Again, I can only relay my personal experience with the issue which is: PPI > code > zero-cost repair based on code.

Should the issue recur and the resolution require anything be done with the ABS control module, I promise to report back.

bluebee · Sep 13, 2010

softtouch said:
My car is currently in the shop and I have no access until Monday. By then, I will provide pictures.

I was re-reading parts here to help someone.

You fixed the car in July but we never saw the pictures.

It would help others because your harness connector is different than mine.

540iman · Sep 14, 2010

agent15 said:
It sounds like both of you are trying to tell me I'm wrong, albeit politely. Again, I can only relay my personal experience with the issue which is: PPI > code > zero-cost repair based on code.

Should the issue recur and the resolution require anything be done with the ABS control module, I promise to report back.

No, we are telling you the experiences we have encountered to try and help others who face the same thing, as well as explain- as best we can- possible reasons for the inability of every diagnostic device that I know of personally having misdiagnosed this error "area"....the trifecta brake lights. No subject likely has as much coverage as it is very frustrating for the average DIY'er, which after all is what brings most of us here, to diagnose using all the standard devices available to not just us, but to indys and techs we have gone to for help. :thumbup:

jeffstri · Sep 18, 2010

This is my first post here. I apologize for it's length and I hope it's taken in the spirit intended (intended to be helpful).

I have a '01 e38 (740il) which has the same ABS/DSC system that many of your e39s have (DSC5.7). I found this thread searching for some insight into my ABS problem: the dreaded brake light trifecta with fault codes that I haven't seen reported here (more about that another time.)

I've perused the entire thread twice and one observation I'd like to make is that there seems to be a misunderstanding of what fault codes mean and how they should be used. Fault codes are not intended to be diagnoses. Whatever scan tool you use, a fault code(s) rarely leads to a solution without more testing. I suspect that the misunderstanding comes in part from the way consumer scan tools such as the OBD scanners Autozone uses, the Peake tool, and Carsoft are marketed.

To give an analogy that's meaningful to me, given my healthcare background, a fault code is like an abnormal blood test result. For example, an abnormally increased white blood cell count (a "fault code") suggests an infection (although it could be caused by other things, and even be "normal"), but it doesn't tell you anything about the site of the infection (e.g., lungs, abdomen, etc) or the organism that has caused the infection, both of which are necessary to treat the infection properly. More information and tests are needed.

Similarly, a wheel sensor fault is not intended to mean that the sensor itself is defective and should be replaced without further testing. It means that the control unit (the DSC module) that monitors the sensor is reporting that it had faulty (or no) communication with the sensor. If the fault code text from a scan tool such as Carsoft is overly specific (e.g., the wiring is faulty), that's probably inaccurate and misleading, and not the same fault description that BMW would use .

The software a BMW dealer uses to read fault codes (INPA, GT1/DIS) also allows measurements (e.g., brake pressure) and activation of various components (e.g., ABS solenoids, pre-charge pump). DIS also provides diagnostic algorithms and tests for translating fault codes into a diagnoses. Modules can be calibrated, coded, and programmed with DIS, SSS/Progman and NCS Expert. WDS provides wiring diagrams, pictures of component locations, module pinouts, and electrical troubleshooting procedures.

INPA, DIS, SSS/Progman and NCS Expert can be be found on the internet, along with excellent instructions for installation and use (http://forums.bimmerforums.com/forum/forumdisplay.php?f=233). All you need is a computer (preferably a laptop) and a diagnostic interface/cable set; I use an "INPA/Edaibas" set that I bought from China on ebay for about $35. WDS can be accessed directly online http://www.bmw-planet.com/diagrams/release/en/e39new/index.htm)

All the above is a preamble to defending the process that agent15 went through and the likelihood that he has in fact solved his problem. What he did was entirely consistent to what is recommended in the WDS:

It's also important to note that reliance on the diode/resistance tests advocated in this thread would probably have indicated his wheel sensor was not the problem and may have led to unnecessary repair/replacement of his DSC module.

bluebee · Sep 18, 2010

jeffstri said:
reliance on the diode/resistance tests advocated in this thread would probably have indicated his wheel sensor was not the problem and may have led to unnecessary repair/replacement of his DSC module.

This is very interesting information.

From the start, we have striven to outline a DIAGNOSTIC test for the shadetree mechanic.

The "diode test" seemed like the best we had.

Perhaps we should dig deeper into "INPA, DIS, SSS/Progman and NCS Expert", all of which I know nothing about so I will defer to others.

The goal will be to supply a DIY that diagnoses the Brake/ABS/DSC trifecta better than what we have so far (i.e., better than the diode test if we can).

540iman · Sep 18, 2010

Welcome! 1st post or 1000th, we are all here to share opinions and experiences. I agree with a lot of what you stated and disagree with a little of what you stated. First, I don't believe anyone (mainly me, I guess) took issue with the way Agent15 went about his diagnostics. I think that a lot of the problem is that Carsoft and others don't, as you say tell you that the patient has a low white blood cell count and stop there. They often "attempt" to go farther and diagnose the patient as having cancer. The last ABS system I repaired was interesting because all I have in the way of BMW-specific diagnostic equipment is Carsoft. The buddy I was working with had INPA, progman, and all the other stuff you mentioned. Both our diagnostics lead to a faulty yaw sensor and NEITHER were correct. Carsoft also said a wheel speed sensor was bad which also was wrong. I determined it was wrong with a diode test. I don't agree with your statement that the diode or resistance test is not conclusive. If you test at the module connector, it is less conclusive then if you remove the suspect wheel sensor-have it and it alone in your hand and then test it with a VOM. You need to make sure that the sensor does not have metal shavings stuck to the end of the sensor and that the wiring to the sensor (between the module and each sensor) is not also what is giving you an open or short.

I think what was being conveyed to Agent15 is to not be surprised if the diagnosis, as given by some equipment, will be wrong and may lead to replacement of parts and the problem will still be there. You must, as you say, get more tests that will further define the problem. Initially, I think I was of the opinion that 90% of the time, problems with the trifecta lights will ultimately be a bad module and 10% a bad sensor. I now think it is more like 70-30. I have found more bad sensors lately, but have NEVER found one that tested bad and was really good or vice verse. I would bet a paycheck that if Agent15 or anyone for that matter has the sensor in his hand and can get meter leads deep into the sensor such that he can test either in ohms or voltage bias forward and reverse (diode test) and the sensor tests bad, that it IS bad. Conversely, if it tests "ok" meaning there is a definite difference when meter leads are reversed and sensor does not test open or shorted BOTH ways- it is NOT the fault.

The main point is that any diagnostic equipment that does not test by going between the sensors and the module simply can not definitively see a bad module from a bad sensor. It is as simple as stating that a blood pressure cuff can not diagnose whether high blood pressure reading at a cuff is because of a faulty heart or a clotted artery. You must somehow get readings I suspect (certainly not a Dr.!) between the heart valves or whatever you do to isolate. If your Indy or dealer hooks up to your OBDII port or your 20 pin and definitively tells you that you have a bad wheel speed sensor, that person is full of doo-doo. Only thing you can diagnose correctly 100% of the time from either of these two points is a bad module due to a communication error or similar. They can not tell a bad input (sensor) from a bad module at these test points.

Car1951 · Sep 21, 2010

Dear Bluebee,

My BMW X5 (2001) turned on three amber light two weeks ago, thanks to your thread I can understand and make a protocol to follow the source of my X5 problem. Just I would like to share with you what my BMW X5 2001 pins sensor changes a little from your publication:

Rear Left 13/29 pins
Rear Right 14/31 pins your tread 30/31
Front Left 28/12 pins
Front Right 15/16

My problem (The best of my knowledge) come from Pressure Sensor, I purchased it but before to replace it I would like to ask you if I need to bleed the rear brake (my digram says that Pressure sensor is connected on the rear brake line of the Hydro unit). In other words; when I will replace the pressure sensor must I bleed the rear brake? Second, are there a tool that we can use at the moment that we need to replace the Pressure Sensor without disconnect the pipe line connected to the Hydro Unit?

I do really appreciate your help, again thank for your valuable threads.

Car1951

540iman · Sep 21, 2010

Bee, you wanna tell him or you want me to? Faulty pressure sensor indication can be another one of those input sensor errors that end up really being the module. You need to back-probe pressure sensor to see what your output is with no pedal pressure and then with pedal pushed hard. It might be your sensor, but just like any other input to the module, unless you physically test that sensor don't be surprised if your error remains. Bad pressure sensors are very uncommon.

Car1951 · Sep 22, 2010

540iman, thank for your observation.

I do really appreciate it. My conclusion is based because without pedal pressure exit volts (Pressure Sensor) is above 4.47 volts? If I can replace the sensor which must maintain 0 Volts with none pressure on the brake pedal, and lineal volts exit depending of the driver pressure? After that you are right should be DSC Electronic modulus.

Car1951

540iman · Sep 22, 2010

good job man!!! you did not say how you tested or arrived at conclusion and many just go by carsoft error or some such crap (and I have Carsoft). You back-probed and did your homework. Good deal. Not sure if it should be zero with no pedal, but you are dead nuts on...it should raise with full pressure toward 5VDC. May be 0-4.5VDC or .5V-5.0 point is that it varies proportionately like you said as pedal pressure changes. G/L:thumbup:

Car1951 · Sep 22, 2010

540iman thanks;

I have arrived above conclusion after have made all test that you and bluebee have suggested. I will need to replace the pressure sensor but there are a little room to do this job because line pipes and location for BMW X5 2001, I don't want to un-install a line pipe I believe that I will need to bleed the system. If I do so.

Brake Pressure Sensor

A brake pressure sensor is installed in the hydraulic unit to determine the degree of pressure build-up for Dynamic Brake Control. It is installed in the front axle brake circuit. The sensor receives its power supply from the DSC control module and produces a linear voltage input signal ranging from 0.5 to 4.5 volts depending on how hard the brakes are applied.

Brake Light Switch (BLS)

The brake switch is an input to the DSC Module to inform it that the brakes are
being applied. If the signal is received during an ASC regulation then brake regulation is interrupted.

I will inform you regarding pressure sensor change.

Car1951

jeffstri · Sep 23, 2010

Car1951, how did you arrive at the conclusion that your pressure sensor might be bad? Did you retrieve any fault codes? If so, what software did you use and what were the codes? Or did you just start doing the tests described in this thread?

If you did get a fault code suggesting a pressure sensor problem and your X5 has DSC 5.7, I suggest you perform the pressure sensor test via the precharge pump described in the WDS:

You will need INPA or GT1/DIS to perform these tests, but you can get the software free and interface and cables for less than $50. (See my post #250 above.) That's a lot cheaper than throwing money at parts based on the voltage test described in this thread, which has never been verified.

I'm struggling with a similar problem right now. I originally got Carsoft code 86 (outlet valve front right) but now I'm getting 115 (ABS/ASC control unit internal error). (I don't find Carsoft errors to be reliable - I'm only reporting them for completeness.)

INPA consistently shows:

and DIS shows:

The brake pressure (measured with DIS) with the pedal not depressed is 0 bar, so DIS says the possible problems are a lose contact or high frequency interference:

I haven't found any loose contact and I have no idea what might be a source of high frequency interference. So I'm going through the WDS "Pressure sensor test via the precharge pump" shown above, but I'm a bit confused by the two statements "Fault currently not present" - I suspect that the second should read Fault currently present. The fault is present after a precharge pump test and the pressure with the engine running and maximum force on the brake pedal is above 80 bar (about 85-100 bar). I can activate the precharge pump with INPA - I can hear it run - but I guess it's output is too low. The only thing I haven't done yet is "ventilate DSC hydraulics," i.e., bleed the brakes with DIS, but it's looking like I'll need a new precharge pump.

In answer to your question about bleeding the brakes, you will need to but it must be done with activation of the DSC module using DIS:

champaign777 · Sep 23, 2010

how your GT1 runs if all 3 lights are off ?
minimum one should be there for sure no ?

540iman · Sep 23, 2010

Your issue sounds like a "classic" example of the module being intermittent and bad. Errors come and go usually with heat. Carsoft as you say just sends you n a direction. If your module is the original, then one of the best $550 or thereabouts expenses is to EAC and a fresh module or at minimum a re-build.
I would not be surprised if both of you guys end up with a new module being the fix G/L. I'm un-subbing from this thread as I think whatever I can lend...I have. BB is now the torch bearer and is as brite a learner and information "magnet" as I have ever run into.

G/L guys & Gals!

Bill

2002 E39 ASC BRAKE ABS lights on => Diagnostic Procedure & Parts Location

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