Help - ASC & ABS warning lights come on intermittently [Archive] - Bimmerfest - BMW Forums

: Help - ASC & ABS warning lights come on intermittently

12-02-2008, 07:50 AM
First, let it be known that I am not much of a DIYer. I've done small stuff like replace the brake light switch and fix the HVAC circuit board but I am not an under-the-hood kind of guy at all. I say this because I did search the forum before writing this post, but the guidance I got on this subject was quite varied and some of it hard to follow.

With that out of the way, I need help figuring out why the ABS and ASC lights come on intermittently in my 1997 M3 sedan. They usually come on after a bit of driving - sometimes 5 minutes, sometimes longer - and then stay on until the car is turned off, which resets them. ABS and ASC work when the lights are off but not when they are on. I haven't noticed any pattern as to when the lights come on; i.e., I haven't noticed that they are triggered by the use of the ABS or ASC, though it's possible that they are and I just haven't noticed it.

I have a mechanic I use whom I trust and his diagnosis was that it might be the ABS control unit. At $1850 to replace the control unit, I feel I need something more concrete than "might be". I do trust and like this guy, but he gets a little defensive/skeptical when I tell him things like "I read on the internet it could be a wheel speed sensor" and doesn't seem interested in checking out other things.

So, any advice?? Other posts on this topic, which are all 2 or 3 years old, include suggestions that the problem might be the ABS control unit, a wheel speed sensor, something on the brake master cylinder, the ABS pump, connectors or solenoids in the ASC system, or a brake pad travel sensor. Are any of these more or less likely than others given my situation (systems still work for a while but then the lights come on and they stop working)? Are any of these things a real novice DIYer could diagnose or rule out (like the wheel speed sensor)? Any suggestions on talking to my mechanic on this? Would I have more luck going to a dealership?

Thanks very much.

12-02-2008, 08:28 AM
Just went through the same process with my 530. You can save huge $$ by having your module repaired, not get a new one.

I wrote it all up, and you don't have to have a lot of skills. Check it out here:

Also click on the August post where I talk about the sensors -- in my case they weren't the problem.

12-02-2008, 08:29 AM
ABS problems are very difficult to assess on DIY basis without any kind of tools that can pull codes. Your research has uncovered about all the possibilities.

I would find a in dependent BMW shop (rather than a delaership) to diagnose the problem. Here is a good place to find on near you:

One place that I don't see on that list taht you might consider is German Motor Werks in Spindale, NC. Talk to John.

12-02-2008, 09:44 AM
i have that same problem on my M... and its a 97 coupe..... were there any recalls on this? would anyone know?

12-02-2008, 12:27 PM
It's a fairly common problem with BMWs, which is why an aftermarket repair business has appeared. That's just one man's opinion, of course.

12-02-2008, 05:47 PM
How about providing more information to help diagnosis your issue. Typically and I mean typically as in this is the usual case but not 100% of the time if you can put the key in the car, start it and no ABS light then it is not your computer of the solinoids it is the sensors. Once you start to move the car and you get the lights then you will most likely find a dirty wheel sensor or poor connection.

Have you pulled the wheel sensors and looked them over? If so did you clean and replace them?

Why go for the most difficult of repairs when the cheapest and simplest path is available. Discount the wheels sensors first then move to the other systems on the ABS and ASC.

More detailed write up of symptoms would help. Has this always been like this, did you do any work around the ASC, throttle body, brake area, etc? That will help. It could be a normal fault of the car but it could be simple too.

Also I totally agree with a previous poster who mentioned that you need a shop with Modic or DIS equipment to read what is going on.

12-03-2008, 11:30 AM
Thanks, everyone. This is all very helpful.

fun2drive: Not sure what additional detail I can provide. The lights typically don't come on until I've been driving the car for a while (and sometimes don't come on at all). I have not done any work on the car (yet) to diagnose/fix the problem, nor have I had any work done on these areas of the car any time recently - really not ever, to my knowledge. This car is my daily driver and is pretty much bone stock and just goes to the shop for routine maintenance and minor repairs once or twice a year. It started doing this several months ago, and the timing of when it began didn't coincide with any particular event or any other problems - it just started doing it one day. It does it more now - probably 75% of the time I drive the car - than it did originally.

Sounds like step one is to get a shop with Modic or DIS equipment to do a reading. Would a typical BMW dealership have it, and should I expect to get charged much for that? Bruce: I prefer independent shops myself and appreciate the link and but it didn't turn up any shops anywhere near me (Charlotte).

Alternate step one sounds like to pull and clean the wheel sensors. As noted above, I am not much of a DIYer, especially underneath the car. Anybody want to offer up a tutorial on "pulling and cleaning wheel speed sensors for dummies"? I did find some stuff yesterday about how to do this (some from Edgy36-39) but it wasn't entirely clear.

Thanks again, all.

12-03-2008, 01:30 PM
as staric said ... i get the same thing... ill be goin to a mechanic soon see what codes he pulls up..

12-04-2008, 07:41 PM
Here is a DIY off my head to do the ABS sensors.
Common caveats apply, don't kill yourself under the car, use good jack stands and jack.
The ABS wheel and sensors are a toothed like wheel that turns when the wheel turns. The wheel sensor is a magnetic that counts the pulses as the wheel turns to tell the car's computer that wheel A is turning at X rpms, wheel B is turning at X rpms, wheel C is turning at X rpms but wheel D is turning at a different rpm. The computer causes the ABS to pulse to get wheel D back in the swing of things.

Ok so first thing to do is to pull the wheel off. To do this put the jack under the car and please not the car's jack but a real jack, take some weight off the car if you are taking off the front wheel and break the lug bolts loose.
The lug bolts are 17mm bolts so use a 17mm socket and rachet. If this wheel is torqued to spec it should be around 80 ft pounds of torque when put on so it will take about 1 1/2 times that torque to break the bolts loose. Remember to turn to the left to loosen these. I don't know your skill level so I will most likely be redundant and if so just skip ahead to the important parts.
Once you have the front wheel bolts broken loose jack the rest of the car up, put a jack stand under the rubber pad that is used to support the car's weight. Lower the jack on to the jack stand with enough clearance to allow the wheel to be removed. For safety I also rejack the car up a little so that both the jack and the jack stand are supporting the car's weight.
Once the wheel is off and if it doesn't want to come off it maybe that the wheel hub has mated with the rotor hub. Because they are dissimilar metals they will rust together if not taken off once in a while. If that is the case use a large piece of wood like a 2X4 and smack the back of the wheel on the rim area. Rotate the rim a little big and smack it again. You may have to do this a number of times until the wheel gives way. This is a common issue on cars that don't get tires rotated frequently. I will now assume you have the wheel off. Now turn the steering wheel hard to the right if you have the left wheel off. It is safe to start the car and use the power steering. You could just turn the wheel before you take the wheel off if you wish skipping this step. Looking at the rotor with the wheel off you will see the rotor and the calipers with pads. Behind the rotor and calipers will be a dust shield, look behind the dust shield and you should see a wire bundle that is not the brake hose that is the wiring for the wheel sensor.
Most likely the wheel sensor hardware will be covered in dirt, grease and oil so use a rag to clean the area. I can't remember on E46's but I think they are the same as E36's. The wire leads to a plug that is held in place by a hex bolt that you will need to remove. Once you remove the hex bolt which is small by the way like maybe 4mm but this from memory so please use the correct metric allen wrench. Oh and it will most likely be bolted down will a lot of force so it will take a lot of force to break it loose. Now remove the bolt and you should have some leverage to twist the sensor while pulling the sensor out. Once you get the sensor out look at the bottom of it and you will usually find a lot of gunk. Just wipe it off and clean the area up as well as cleaning the sensor cylinder the sensor goes in and the sensor barrel itself.
As they say the installation is the reverse of the removal.
On the rear tires you don't need to keep some weight on them when you go to remove the lug bolts. The transmission and emergency brake will hold the wheels from turning. If you find the wheels rusted to the rotors apply a very light coating of antiseaze to the hub area after cleaning it up. That will make removing the wheels much easier in the future for whoever removes them.

Now once you do this you will know that you don't have a wheel sensor issue unless the wiring is compromised someplace. This is the perfect time to just trace back with your hand where the wiring goes and if all seems in order then most likely you have intact wiring...

12-04-2008, 08:09 PM
i had that experience with my truck, and because the abs module is under the radiator reservior, unfortunately mine got leaks it goes right down to the module, since coolant is oil base, it soak wire connectors so i got that problem time to time until clean/pray it with hot water and let it dry and somehow it goes away,

try it, could be relevant.

good luck my friend

12-05-2008, 06:14 AM
I've done this on the 530 not the M3, but I'll bet there are similarities. You don't need to be a mechanic -- I replaced both front sensors before I figured out it was the module. Don't mind though, now they should last life of car. BTW, if you somehow do need sensors shop online -- found mine for around $60.

BMW dealership will charge you around $100 to read the code, in case that question hasn't been answered. And, there's no guarantee the code will be accurate. For example, my indie mechanic told me the code said left front sensor, but replacing it didn't solve problem.

You could save yourself some work by sending the module in. If there isn't anything wrong with it, BBA will only charge you postage.

Here's where the sensor connects to the back of the hub on the E39, the "fusebox" that it fits into, and picture of sensor itself.

12-06-2008, 07:10 PM
Can something like a broken sensor stop you from getting the car inspected? Thanks

12-11-2008, 07:11 PM
Great words by all. Question for Staric - did you just get the ABS and DSC lights or did you also have issues with the speedometer/odometer. I'm trying to peg down a similar issue.

12-12-2008, 03:12 AM
I have the exact same problem with the OP and he seriously couldn't describe it better. It's just one day the lights started coming on and you cant turn them off unless you turn off the car. Then you turn the car back on and they work fine (until they go out again) I have found its around 10 minutes of driving but it has happened in less than 4 and not at all (more than 2 hours) I haven't actually cared too much but now it is happening more and more often. I have a 1994 325is and I'm 16 so I have a low budget. But I'm just explaining my problem, hope you guys can diagnose it. Thanks.

12-18-2008, 05:50 AM
Buster: For me, it's just the ABS/ASC lights - no other problems at all.

Only update so far is that I found a local shop with the right diagnostic equipment but when I took the car in, wouldn't you know it - the warning lights weren't on that day, which they need to be for them to diagnose the problem. I plan on taking it by again tomorrow or next week, assuming the lights come on when I am heading over.

01-30-2009, 07:47 AM

I found a shop that said they had the right tools and finally got around to taking it by one day when the lights were on. They were unable to confirm the problem for sure but "suspect" it's the ABS control unit. One question I have now is whether I need to find a shop with different scanning tools or if what they've said makes sense.

They used a Launch X431. The printout from the machine says at the top it found 2 total codes: "17 - Fault in the power supply of all solenoid valves or operations of front left inlet valve faulty" and "132 - Pedal travel sensor signal not sent or faulty." The rest of the printout just goes through diangosis of the stop light switch at various pedal positions and confirms that everything is fine with it.

The guy who ran the tests told me that he had some trouble getting my car to communicate with the scanner but that he was able to confirm that I don't have a wheel sensor problem, though he didn't say how he was able to eliminate that possibility.

Replies to my earlier post suggested finding a shop with Modic or DIS equipment. Is the Launch X431 different and, if so, did I screw up not finding a shop with that specific type of equipment? I didn't ask about the exact type of scan tool they had when I first spoke to them, but they did assure me that they had the specialized tools necessary to diagnose my problem.

If it looks like I'm stuck with an ABS control unit problem, which I'm being quoted $1500 or more to replace, does anybody have thoughts on getting them repaired through places like Module Masters or BBA Remanufacturing? "Edgy36-39" suggested this last time (thanks!). The Module Masters website suggests the control unit on this model is unrepairable. BBA Remanufacturing said I need to check what "series" control unit I have but suggested they think they can fix. I just spoke to them on the phone and since I won't be able to check the car until this weekend and also understand it may be tricky to access the unit to find out what kind it is, does anyone here know? Thye say it needs to be a series 0265900xxx ir 0265950xxx. If it's not, they'll still look at the unit and take a stab at fixing it (and actually do so for free) but aren't optimistic about success. Is the ABS control unit pretty easy to access and get off? The person I spoke to suggested maybe it's not. Also, where the heck is it?

Any further feedback most appreciated.

01-30-2009, 10:36 AM
Ive used the Launch System when i worked as a mechanic. for about a year. its a great tool... works wonders... btw im still having this issue. ill be going home today to clean the sensors to see if that makes a difference.


01-30-2009, 06:37 PM
By all means do the pedal sensor first and foremost. You can have the ABS unit pulled and rebuilt and I have seen a DIY on it as well in
The pedal travel sensor is a common problem and is much cheaper to fix then the others are.

My suggestion is to do the pedal sensor and see how it goes....