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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 01-05-2015, 12:37 AM
Tepa Tepa is offline
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1999 E39 ASC and ABS lights - sensor or ABS module?

Hello,

About 4 days ago my 1999 E39 520i (113 000km, manual) became a victim of the bifecta. I know there is loads of information regarding this issue and I've read them and followed the diagnostic procedures. However, I seem to be in a dead end and I'd like your opinions on this. The rear right sensor has been changed 2 years ago.

At first the lights would only come up after approx. a few minutes or ~1km of driving. And until the lights come on, the ABS is clearly malfunctioning by activating on the slightest breaking etc. However, since yesterday the lights have sometimes gone on at the startup.

I've used my cable and INPA to read codes:
code 66 power supply engine speed sensor, control unit error

I tested the sensors with DMM (diode and resistance) and got normal results for the left rear and the right front sensors. I should also mention that speedo etc. are working normally.

For the right rear sensor I was unable to get a diode reading, but resistance was normal and cruise control is working. I also could not get a diode reading for the left front sensor and what caught my eye was that the resistance was veeeery small, a fraction of the normal resistance and clearly different from the other sensors. I have a spare front sensor which I hooked up (didn't install it) and the resistance turned to normal values - still no diode reading. This new sensor is not OEM and I've read that they might not give out a diode reading at all - or they can be just faulty from the beginning.

So.. What am I looking at here?

I'm thinking:

a) According to the DMM test it should be 2 bad sensors (but still cruise is working..). I'm not an expert here and the lack of diode reading could be because of that. However, I got reliable results from 2 other sensors repeatedly.

b) Could it be just the front left sensor? I need another visit to garage and a better allen wrench to be able to actually install the sensor.

c) Should I send the ABS module to be fixed?

Thank you for any help!

FYI: I made a similar post a few days ago, but it never appeared here.
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  #2  
Old 01-06-2015, 05:49 AM
Tepa Tepa is offline
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Bump.

Currently the lights may or may not come on at startup, but anyway they come on quite soon after driving.
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  #3  
Old 01-06-2015, 06:58 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by Tepa View Post
Currently the lights may or may not come on at startup, but anyway they come on quite soon after driving.
You seem to have read the references, but I will just re-quote the canonical one for others reading this thread:
- How to diagnose the BMW amber ABS BRAKE DSC/ASC trifecta or bifecta (1)

The procedure, as you clearly are aware of, is to first test the four wheel speed sensors, and then test the ABS control module (or send it out for repair).

It seems you're having trouble getting readings on the four wheel speed sensors, so, you're still in the initial phase. Bear in mind that you can test the sensors at the wheels in addition to at the harness. Also bear in mind that there are multiple tests (some of which you have run). All of these tests are discussed in the reference above.

Also, as you seem to be aware of, sometimes sensors just don't test well, so, take a look at this thread, if you haven't already:
- Quick99Si's explanation of why the 10-minute wheel speed sensor diode-action quick test doesn't always work (1) (2)

Moving on to the ABS control module, as you are probably aware, the problem almost all the time is that the 7th aluminum wire lifts off its gold bondpad, which changes something (perhaps the increased resistance is causing a voltage drop) - which makes the ABS computer do funny things.
- How to diagnose and repair the ABS control module (1)

As you are already aware, the intermittence is thought to be due to the wire lifting up off the gold bondpad with heat.

As you probably know, the hair-dryer test has been used to prove that the 7th wire is loose, as has the toothpick test (which is conclusive).

All this is a repeat of the first thread I linked above, so, I really can't point you to better information than that.

If you determine the ABS control module is bad, then read this thread:
- What are all known options when your ABS control module is bad (1)
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See also: E39 Bestlinks & How to easily find what you need

Last edited by bluebee; 01-06-2015 at 07:32 AM.
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  #4  
Old 01-06-2015, 07:18 AM
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johnstern johnstern is online now
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Intermittent problems usually point to a failed ABS module or wire damage under the car. The rear sensors seem to the OK as the speedo and cruise are working. There is no mention as to what transmission you have, but if you have an auto, the RF sensor sends speed data to the trans and if it was bad, you'd get a trans in failsafe mode message/code.

The fact that the LF sensor has low resistance would make me want to make sure that the LF was working. You'll either have to install your spare sensor at the LF to see if there's any difference in performance or ABS fault codes. However, if the present sensor was at fault, you'd get a code saying so.

Since you have an ABS code that references module power problems (see Bluebee's post above) and the failure is intermittent, I'd bet that your module needs repair.
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  #5  
Old 01-07-2015, 01:01 PM
Tepa Tepa is offline
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Thank you for your answers!

After further reading and studying my primary suspect is the abs module as there are not so many symptoms that would indicate a bad sensor. However, I decided to take the car to a local BMW expert who is better equipped to trace the problem and give me a proper diagnosis. I have an appointment on Jan. 15th and I will update this thread as I have more info about this.

I suppose I will have to send the module for a repair, though. Fingers crossed that it is a repairable one.
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  #6  
Old 01-07-2015, 03:50 PM
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Quote:
Originally Posted by Tepa View Post
I decided to take the car to a local BMW expert who is better equipped to trace the problem and give me a proper diagnosis
Most (all?) techs give the wrong answer, simply because they don't know what we know, which is explained by 540iman many times in the bestlinks ...

- Explanations by 540iman as to why the fancy diagnostic tools very often (extremely often, like almost all the time) fail to properly diagnose the trifecta or bifecta (1) (2) (3) (4) (5) (6)

So, if you still want to take your bimmer to the mechanic, ask them WHERE they hook up their test leads.
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  #7  
Old 01-08-2015, 01:00 AM
Tepa Tepa is offline
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Thank you for the tip!

I will take the car to the mechanic as it doesn't cost too much to have him do proper diagnostics (not just reading the codes). He seems to be familiar with older BMWs and their ABS problems.

I'm not letting him replace any parts unless he can assure me that it is a sensor issue.

Again this morning the lights didn't come on until I had driven a few minutes. To me this really seems to be an issue with the abs box.

And sorry for forgetting this information: the car is manual. When the RR sensor was bad 2 years ago, the car would go into limp mode. Luckily this hasn't been an issue now.
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  #8  
Old 01-08-2015, 04:07 AM
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Quote:
Originally Posted by Tepa View Post
Thank you for the tip!

I will take the car to the mechanic as it doesn't cost too much to have him do proper diagnostics (not just reading the codes). He seems to be familiar with older BMWs and their ABS problems.

I'm not letting him replace any parts unless he can assure me that it is a sensor issue.

Again this morning the lights didn't come on until I had driven a few minutes. To me this really seems to be an issue with the abs box.

And sorry for forgetting this information: the car is manual. When the RR sensor was bad 2 years ago, the car would go into limp mode. Luckily this hasn't been an issue now.
Not necessarily. I have had a front and a rear wheel speed sensor go bad. Both times it caused random ABS failures that became more and more frequent. In both cases it was the sensor wire insulation crumbling apart and shorting out the sensor. Apparently after over 25 years of service the plastic sensor material starts to give way. The front sensor literally crumbled entirely apart when I removed it. The rear sensor, only the wire insulation was crumbling.
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  #9  
Old 01-08-2015, 07:54 AM
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Quote:
Originally Posted by Flybot View Post
In both cases it was the sensor wire insulation crumbling apart and shorting out the sensor. Apparently after over 25 years of service the plastic sensor material starts to give way. The front sensor literally crumbled entirely apart when I removed it. The rear sensor, only the wire insulation was crumbling.
Had the same thing happen when I took the outer casing off and I was going to solder and heat shrink tubing this...


And BTW, DON'T make the mistake I did and buy a $40 Delphi ebay wss. Spend the $100+ dealer part made by Siemens and be done for another with that sensor for another 10+ years.
You can see the biggest reason why the Delphi would NEVER have work vs. the Siemens/dealer (bottom) works.
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Last edited by e39 crackr; 01-08-2015 at 08:04 AM.
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  #10  
Old 01-08-2015, 10:44 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by e39 crackr View Post
Spend the $100+ dealer part made by Siemens
This is good information for the thread:
- What parts to only buy OEM (1)
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  #11  
Old 01-19-2015, 07:25 PM
dannyman939 dannyman939 is offline
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Schmidtt trigger voltages

Quote:
Originally Posted by Tepa View Post
Hello,

About 4 days ago my 1999 E39 520i (113 000km, manual) became a victim of the bifecta. I know there is loads of information regarding this issue and I've read them and followed the diagnostic procedures. However, I seem to be in a dead end and I'd like your opinions on this. The rear right sensor has been changed 2 years ago.

At first the lights would only come up after approx. a few minutes or ~1km of driving. And until the lights come on, the ABS is clearly malfunctioning by activating on the slightest breaking etc. However, since yesterday the lights have sometimes gone on at the startup.

I've used my cable and INPA to read codes:
code 66 power supply engine speed sensor, control unit error

I tested the sensors with DMM (diode and resistance) and got normal results for the left rear and the right front sensors. I should also mention that speedo etc. are working normally.

For the right rear sensor I was unable to get a diode reading, but resistance was normal and cruise control is working. I also could not get a diode reading for the left front sensor and what caught my eye was that the resistance was veeeery small, a fraction of the normal resistance and clearly different from the other sensors. I have a spare front sensor which I hooked up (didn't install it) and the resistance turned to normal values - still no diode reading. This new sensor is not OEM and I've read that they might not give out a diode reading at all - or they can be just faulty from the beginning.

So.. What am I looking at here?

I'm thinking:

a) According to the DMM test it should be 2 bad sensors (but still cruise is working..). I'm not an expert here and the lack of diode reading could be because of that. However, I got reliable results from 2 other sensors repeatedly.

b) Could it be just the front left sensor? I need another visit to garage and a better allen wrench to be able to actually install the sensor.

c) Should I send the ABS module to be fixed?

Thank you for any help!

FYI: I made a similar post a few days ago, but it never appeared here.
Not saying that I am an expert, but for all the testing you guys are describing let me ask a question?

Have the wheel sensors ever been replaced to your knowledge? The front sensors are extremely prone to failure due to their relationship to steering and cable failure. Over time, the insulation will crack and the wiring will be exposed to the elements.

The S/N (signal-to-noise) levels for this circuit are very sensitive to impedance drops, not much to forgive to operate properly.

The sensor set of 4 cost me $40 on ebay and the replacement took one hour.
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  #12  
Old 01-19-2015, 11:39 PM
Tepa Tepa is offline
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Quick update:
I took the car to the mechanic, but didn't leave it there for a diagnosis; as I explained the symptoms and what I've done so far, he became convinced that the ABS unit is to blame here. The mechanic has done a lot of repair work on these particular abs units so I'm trust his opinion on this. According to him there should definitely be a clearly sensor related error code if the fault was not in the unit. However he said that in a rare case it could be a wiring issue, which has been said in thread also.

So now I'm sending the unit for a repair (costs 220 +posting fees) and if they do not find a fault in the unit they won't charge anything. If they do not find a fault in the unit, I will try swapping the left front sensor.
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  #13  
Old 01-28-2015, 08:41 AM
Tepa Tepa is offline
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Exclamation

Updating and bumbing, need your opinions again.

The ABS unit came back today - healthy. They inspected it, hooked it on testers and the unit is ok. Well, at least it only cost about 50 and now I can be sure of the unit's condition...

But obviously it means that I still have to figure out the real problem. I just installed the unit back and before doing so, I cleaned the connectors with electronics cleaning oil. Then I started reading codes and of course there was a fault for each speed sensor, because the car was driven without the ABS unit.

I cleared the codes and decided to finally do a live data test. I managed to get the laptop in to the car and then I went for a drive only to see this...



Also, no more error 66, but an error code for the front left sensor. The one that had low resistance readings and no diode reading. The one that I already tried to replace. I even returned the spare sensor I had already bought.

Do you think I can trust this error code now? I believe the ABS unit may have been kind of "rebooted" when it was opened and tested and maybe the fact that I cleaned the connectors could have something to do with this.

And is it necessarily the sensor itself or could it just be that the sensor is unable to get a reading from the ring due to dirt or something? Actually this is what the BMW mechanic first suspected when I told him about this on the phone.
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  #14  
Old 02-02-2015, 12:46 AM
Tepa Tepa is offline
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Bump!
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  #15  
Old 02-02-2015, 04:56 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by Tepa View Post
The ABS unit came back today - healthy.
We can't second-guess an ABS rebuilder, whom we must assume has test jigs that we can't hope to have, so, at this point, let's assume the ABS control module is working.

- What are all known options when your ABS control module is bad (1)
Quote:
Originally Posted by Tepa View Post
an error code for the front left sensor. The one that had low resistance readings and no diode reading.
Normally, I don't trust any error because the diagnostic reader is often reporting what a faulty module is experiencing; however, given you know you have a good "computer", then this error code should carry more weight than normal (where, in normal cases, it carries nearly zero weight).
- Repeated explanations by 540iman as to why the fancy diagnostic tools very often (extremely often, like almost all the time) fail to properly diagnose the trifecta or bifecta (1) (2) (3) (4) (5) (6)


Quote:
Originally Posted by Tepa View Post
Do you think I can trust this error code now?
I, for one, don't know, but, there are quite a few tests you can run on a sensor, and you can swap sensors on an axle, so, there's plenty you can test.

In addition, there are over 20 sensors that innervate the traction control system, but usually they're OK.

Quote:
Originally Posted by Tepa View Post
could it just be that the sensor is unable to get a reading from the ring due to dirt or something?
Sure. Lots of people clean their sensors and pickup rings.

You can test for pickup you know. For example. one of the tests involves spinning the wheel and watching the pulses, for eample.
- How to diagnose the BMW amber ABS BRAKE DSC/ASC trifecta or bifecta (1)


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Please read the suggested threads, where the best always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #16  
Old 02-03-2015, 05:36 PM
lsrguy98 lsrguy98 is offline
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Which rear sensor controls the cruise control? Is it the Passengers side rear or the Drivers side rear?
Thanks.
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  #17  
Old 02-04-2015, 06:29 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by lsrguy98 View Post
Which rear sensor controls the cruise control? Is it the Passengers side rear or the Drivers side rear?
Thanks.
I'm sure it's in this canonical thread for your model year:
- How to diagnose the BMW amber ABS BRAKE DSC/ASC trifecta or bifecta (1)

For my 2002, it was this:
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  #18  
Old 02-05-2015, 04:40 AM
lsrguy98 lsrguy98 is offline
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Thanks Blue. Is the right rear the passengers side rear as if you were sitting in the car?
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  #19  
Old 03-04-2015, 06:36 AM
Tepa Tepa is offline
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I'm sorry for the delayed reply. I have been busy at work, but today I finally managed to take the car back to the mechanic.

We lifted up the car and found that the sensor had sort of "corroded" off. More specific explanation here:
The part of the sensor that mounts the sensor against the wheel assembly, first becomes just a little bit loose on one side. As time goes by this "hole" gathers aluminum, dust etc. dirt and eventually the dirt pushes the whole sensor assembly away from the wheel assembly and obviously from the ring itself too. Hence it stops getting a reading and shows a steady 2kmh reading in livedata. Basically there's nothing wrong with the sensor itself (except that the mounting part has broken), but it simply can not get a reading from the ring. I would estimate that my sensor was pushed off for only a few millimeters - it does not require much for this to happen.

This is a problem with the front sensors. The mounting is a bit different on the rear sensors.

The mechanic removed the sensor, cleaned off the dirt and the ring and finally installed a new Bosch sensor.

All in all this operation was 150 and 45minutes for a pro.

So this is one possible scenario for the bifecta. However, I still do not know if the original error code "Error 66" was a cause of dirty ABS connector: after the ABS unit came back from inspection and I cleaned the connectors and installed the unit back, the error code changed to indicate a fault directly in the left front sensor.
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