[Big Chaze]

If my speedo and cruise work intermittingly, Lets say when I use a multimeter to check my sensors, if at the time my sensors are in the "working" phase, will this make things more difficult to diagnose? Sometimes I have speedo and cruise, and sometimes I dont...sometimes I have either or, and sometimes neither.

Is there a way to check what the module is sending to the sensors? Will this vary if things arent working properly? Will the multimeter reveal anything?

 

[Trebbia]

Sometimes I have speedo and cruise, and sometimes I dont...sometimes I have either or, and sometimes neither.

It's very common for the abs trifecta to be intermittent.

What are your voltage diode style readings on the four sensors?

And, did the dental pick show the wires lifted inside the abs computer?

 

[Big Chaze]

Havent gotten around to all that yet...Im waiting on my obd cable to come in to mess around with inpa. Dental pick??? thats a new one...elaborate please..

 

[Quick99Si]

Havent gotten around to all that yet...Im waiting on my obd cable to come in to mess around with inpa. Dental pick??? thats a new one...elaborate please..

Cut open the ABS module and use a sharp tool to see if the relatively large wires (still very small!) have lifted off the solder points. This is just about 100% confirmation that your ABS module is your problem.

 

[Big Chaze]

Cut open the ABS module and use a sharp tool to see if the relatively large wires (still very small!) have lifted off the solder points. This is just about 100% confirmation that your ABS module is your problem.

Cut open?? Then what if its not the module?? Does it snap back into place?and solder points??? Will I be able to solder those bad boys back on?

 

[Quick99Si]

Cut open?? Then what if its not the module?? Does it snap back into place?

Cut open, glue/seal shut

 

[Big Chaze]

but what about the intermittent functioning of the cruise and speedo?? If the contacts were affected the way you say, there wouldnt be any intermittent anything, correct? I would not have cruise and speedo all the time, dont you agree?

 

[Quick99Si]

but what about the intermittent functioning of the cruise and speedo?? If the contacts were affected the way you say, there wouldnt be any intermittent anything, correct? I would not have cruise and speedo all the time, dont you agree?

The fact that it's intermittent is an indication to me that the ABS module is your source of troubles. You may not have noticed it yet, but whether or not those functions work is probably closely linked to the temperature in the engine bay (vibration may also cause it, so it isn't an exact science just yet). You may be able to make it "fail" more quickly by using a heatgun on the ABS module to get it nice and hot.. however, as time goes on, it pretty much seems to get a mind of it's own which only complicates the troubleshooting procedure. I suspect that the module's proximity to the exhaust manifold is the primary cause of premature failure of the ABS/DSC systems in ours cars, E38's, and some Volvos.

Keep in mind that the ABS module is the central point of processing for the inputs (speed sensors, steering angle sensor, lateral acceleration, etc) and outputs (vehicle speed, ABS control, DSC, etc). Speed sensors provide a square wave to the ABS module, and the module sends the speed data via BUS. That is to say that intemittent operation of the speedometer can easily be attributed to an intermittently failing ABS module. Pull the module out and you'll notice that your speedometer, odometer, cruise, ABS/DSC, speed-controlled radio volume/door locks and everything else will also stop working. When those broken contacts inside disconnect, the module shuts itself off and functions the same as if it weren't connected at all. Problem is, a bad speed sensor in the front(?) can also cause it to shut itself down -- see my created threads for some good info on my own troubleshooting, symptoms, errors, etc..

I have done more than my fair share of research and testing with regards to this issue, and I have YET to find a symptom or test that can conclusively and consistently tell you if a speed sensor or module needs replacement... that is, unless you do some logging in INPA or GT1 + using your brain.

 

[MJB9]

If you swing by Chicago, I can hook up your car to my laptop to help narrow down the problem. Peake will not tell you which, if any, speed sensor has gone bad, unfortunately. The brake pressure sensor is very easy to test with either a multimeter or INPA/GT1, as is the steering angle sensor (laptop only AFAIK). I suggest taking off the speed sensors and giving them a nice cleaning because your problem likely lies there. Assume the module is good but do not discount it as a potential cause down the road.

In related news, my buddy with 130k just started getting the same problem. His is definitely a bad module and is looking for a place to do the rebuild for him in the coming days. Anecdotally, 6-cylinder cars seem to last longer than 8's...

Hi. Thank you very very much for the offer. It's a bit too far (7 hours round trip), and with gas at $4/gal., I'm either gonna go dealer route ($65 to read codes), or re-buy bavarian technic. But sincerely thank you! Folks on here are the best! I've been searching for a multimeter test procedure for the pressure sensor. It's been an illusive search/find so far, but will keep looking.

As for your buddy, I used autoecu.com via ebay and it was $99 shipped. It looked good when I got it back. And yes, I'm hoping v6 last longer because I have 175k miles

Michael

BTW. I've seen several posts of failed DMM testing, including mine. I was wondering for those with successful results, if they can post the DMM they used. I have a rad shack one. it's probably 5 years old, but works perfectly in my day to day electronics/electrical work. I've even tested on a spare resistor and diode, and readings are as expected--just not when in a BMW ;-) I'm not ruling out that some DMM's just won't work in our bimmers. I'm open to buying one and trying it though.

 

[bluebee]

Does it snap back into place?

Everything you need to know about opening & closing the ABS control module is here:
- Bill's ABS autopsy thread

Dental pick??? thats a new one...

Actually it's not new at all.

The diagnostic technique is already discussed ad infinitum in this thread (dental pick, toothpick, etc.).

These are the wires most often implicated:

but what about the intermittent functioning of the cruise and speedo??

It's intermittent for many of us.
There's not much diagnostic value in the intermittence in and of itself.
Quick99Si gave a great explanation of why above.

I've been searching for a multimeter test procedure for the pressure sensor. It's been an illusive search/find so far, but will keep looking.

You're not the first person to say that but it perplexes me to hear that because I typed /pressure sensor in the bestlinks and I found this in less than a second or two:
- How to run a ABS BRAKE DSC trifecta brake pressure sensor diagnostic test (1)

I used autoecu.com via ebay and it was $99 shipped.

I echo what Quick99Si said about the diagnostic tools.

See also this thread:
- The most often recommended BMW diagnostic tools & cable interfaces (1)

I've seen several posts of failed DMM testing, including mine.

Here's Quick99Si's explanation:
- Why the 5-minute ABS DIY quick test doesn't always work, especially on brand new non-OEM wheel speed sensors (1)

I was wondering for those with successful results, if they can post the DMM they used. I have a rad shack one.

My 30-year old Fluke 75 worked perfectly:

Here are my results using that DMM:

PS: I apologize that all the information above is already in this thread; these are all repeat questions which are already answered in this thread ... so I gave the same answers given before in this thread.

 

[Big Chaze]

Everything you need to know about opening & closing the ABS control module is here:
- Bill's ABS autopsy thread

Actually it's not new at all.

The diagnostic technique is already discussed ad infinitum in this thread (dental pick, toothpick, etc.).

These are the wires most often implicated:

It's intermittent for many of us.
There's not much diagnostic value in the intermittence in and of itself.
Quick99Si gave a great explanation of why above.

You're not the first person to say that but it perplexes me to hear that because I typed /pressure sensor in the bestlinks and I found this in less than a second or two:
- How to run a ABS BRAKE DSC trifecta brake pressure sensor diagnostic test (1)

I echo what Quick99Si said about the diagnostic tools.

See also this thread:
- The most often recommended BMW diagnostic tools & cable interfaces (1)

Here's Quick99Si's explanation:
- Why the 5-minute ABS DIY quick test doesn't always work, especially on brand new non-OEM wheel speed sensors (1)

My 30-year old Fluke 75 worked perfectly:

Here are my results using that DMM:

PS: I apologize that all the information above is already in this thread; these are all repeat questions which are already answered in this thread ... so I gave the same answers given before in this thread.

Great...thanks. Just to clarify, my trifecta lights are always on regardless of a cold or warm engine,...it's my speedo and cruise that work intermittingly.

 

[bluebee]

it's my speedo and cruise that work intermittingly.

Oh. OK. My mistake.

I had misinterpreted the intermittence to be the ABS/BRAKE/DSC trifecta lights ... and not the actual gauge and stalk operation.

The speedometer is innervated by the left rear wheel speed sensor and the cruise control by the right rear wheel speed sensor ... so ... I'd suggest you run the ten-minute DMM test to compare those to what you get at the front sensors.

It would be rare for 'both' rear wheel speed sensors to go bad at the same time - but if they were, swapping them might not show any difference (if they're both bad).

Still ... the hour spent might be worth the effort after you do the ten-minute DMM test.

PS: You don't need to quote my whole post, with pictures, as it makes it hard to read for the user. I'd suggest you simply edit my quote down to the essential like I did with yours.

 

[Big Chaze]

PS: You don't need to quote my whole post, with pictures, as it makes it hard to read for the user. I'd suggest you simply edit my quote down to the essential like I did with yours.

Youre the like the Forum God..:bow:

I will start doing research on the dmm test

 

[MJB9]

Bavarian Technic says it's code 81 (Pressure Sensor Lead). If I can find a volunteer walking by saturday, I tried the DMM but since I live alone, it's too much. I am assuming the sensor is in fact bad. However, searching for a repair/replacement DIY for the pressure sensor seems to be as elusive as the pressure sensor threads initially were. I believe I know why me/others have had a hard time searching for pressure sensor threds (but no issues searching other topics). I believe because many of those postings are of pictures only (and the text is embedded in the picture), so there is nothing to search for a keyword (or at least very little). I've been googling and searching the forums, but have yet to find a DIY on pressure sensor replacement. I found two primitive links that give no DIY direction, including bleeding (or not) of the brakes. Anyone replace a brake pressure sensor on a 2002 e39 525i before?

The only two not so useful links I've found are:
http://tis.spaghetticoder.org/s/view.pl?1/06/55/93 and
http://tis.spaghetticoder.org/s/view.pl?1/07/64/36

 

[Pappa Bear]

So I just read this whole thread, my head is spinning, but i think i have found my problem. But just to be sure, let me share my symptoms and see what yall have to say. I am throwing a code 90, Intermittent system down. When driving any or all of the following may happen, usually they are set off by hitting any sort of bump in the road, like a bridge joint, but rarely, maybe never, happen when driving slowly over smooth pavement (happened twice in 5 miles of open highway but never in 45 minutes of <10mph traffic):
Engine failsafe prg, accompanied by the DSC, Brake, and ABS lights as well as a pulse of the brakes occur all at once, but it clears up after a half second and the car drives fine.
DSC light flashes even when not activated, like when driving straight on the highway not making any turns, accelerating or braking.
Brake light and ABS light on dash illuminate intermittently.
Radio head unit cuts out for 5-10 seconds.

So, are we thinking this is the ABS module? When I had the codes read no wheel speed sensor codes were stored.

I hate electrical gremlins...

 

[Pappa Bear]

...

 

[geobrick]

...usually they are set off by hitting any sort of bump in the road, like a bridge joint....

You may have a combination of things but when my ABS was triggered while slowly going over small but solid bumps (like the track for a sliding gate or in your case a bridge joint), it turned out to be warn or leaking thrust arm bushings. There are several DIY threads on that.

You described several other symptoms that aren't typically related to the thrust arm bushings but it might be a good place to start.

 

[Pappa Bear]

It's possible that could cause some extra wheelslip for a second but I would think the computer would have tolerances built in for that. I have aftermarket urethane bushings but they are getting kinda old. So yes they may need a checkup.

 

[MJB9]

UPDATE: Not having much luck. The pressure sensor didn't fix it. Off to Boston tomorrow as is. Another let down. Of course in hind sight I'm kicking myself for not taking a chance/trying hard to shove DMM leads into back of pressure sensor connector and do the test, but the spongy inside was hard to penetrate and I didn't want to expose the inside of connector to future corosion. Plus I live alone and couldn't find anyone to help. So, so far, replaced ABS module that was never bad to begin with, and ATE never did say if defective, only that they bring it up to spec. And not the pressure sensor. Still get code 81 (sensor pressure). Actually mine says sensor pressure lead which is interesting if it was telling me a bad wire. But these are BMW/Bosch codes and my understanding it 81 is pressure sensor (period), no lead at the end. I tried resetting the code and it comes right back. I'll have to do more research but sounds like possible the pre-charge thing? But the symptoms described here that led me to replace sensor was that the pre-charge happened at or 30mph or so. My lights are on all the time. Although, before the module was rebuilt, the lights ONLY, and repeatable, came on after car was warm. Then while driving without the module, all three lights all the time, and the check engine light. Once I got the module back on, the check engine light went out within 10 miles of driving. Since then, they never go off-even when cold. AFter that, I bought the bavarian tech and it told me code 81. Now that is replaced $140 later (I did find one for $120), but it was not in stock and I was wanting it before I left for Boston.

Also interesting was that while unscrewing the sensor, there was zero, and I mean zero fluid that came out of the DSC unit. Another posting http://www.xoutpost.com/bmw-sav-forums/x5-e53-forum/81722-dsc-pressure-sensor-replacement.html mentioned very little, but I got zero. The old sensor was slightly wet, but that was it. I did not bleed as a few others have/have not. And since I got zero fluid coming out, quickly put the new one one. Brakes are fine, but all three lights still. :-(

For FYI, I used a 15/16" deep socket. I tightened till it stopped and then a hair more. It's not like a spark plug where you keep going, this I could tell it was time to stop. You could easily use an adjustable wrench. It comes off with little force. The new sensor is the last pic (shiny one).

But alas, no fix for me. On the bright side, I have an expensive paperweight (the original, but working pressure sensor).

Could the module that was rebuilt be sending a bad code (ATE from ebay)? Has anyone had a module rebuilt that was bad? How did you find out? I have heard units with 002 (mine) were problematic, but I would have thought ATE would have told me if there was an issue?

 

[MJB9]

While prepping car for my trip to Boston, checking and filling fluids, I noticed some wetness under the what I think is the precharge pump. While it's possible fluid came out when I took the sensor out, I'm 99.99% certain none did. I watched very closely. However, it is possible that while the deep socket was on, adn while tightening, some came out and I missed it. It's also possible that it was runoff from filling up the washer fluid the otehr day (but doubt it as it would have dried up by now). It's also possible the unit is leaking. Aside from the precharge symptoms of failure I read about driving around 30mph (which I'm not experiencing), I heard someone say that if you slam on your brakes and car responds immediately (like stopping for a deer), it's not the pre-charge. I'm not a mechanic so not sure about that. However, about a week ago, someone cut in front of me and I had to hit the brakes VERY hard to avoid an accident. There was smoke (from one of the tires--maybe more), but the car stopped VERY good considering no anti-lock. And while I didn't go to that extreme tonight, the brakes work awesome. Since I've already thrown money at two parts that were not broken to begin with, I hate to replace the pre-charge too, but running out of things to replace. lol.

The pics arent' great. It's from my phone, upside down, and hard to get it in there. The last two pics are the closest but in person is more revealing. The wetness could also be from a deal bleeding the brakes, but doubt it as I don't think they'd go near there. I'm guessing there's a minor leak under precharge, but that I do not think would explain the code 81. Nor that the reservoir is 100% full. Actually, overfill--thank you dealer for the flush and overfilling it.