Bmw ABS and ASC Fault Lights!

Can anyone help? My abs and asc fault lights have appered on the dash, after speaking to someone a bit technicle they told me it would proberbly be a speed sensor! Can anyone tell me if this maybe true,
where its located, and could i do it myself? The car is a 523 (1988) E39 Thanks!
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There's one on each wheel near the bearing. Trouble trouble is working out which is dead.
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Yes, it is probably true. There are speed sensors on all 4 wheels. You can do it yourself very easily, assuming you can change the brakes by yourself. The trouble is, the sensors cost about $90 (USD) each, and they are different for front and back. You need a system diagnostic to determine which is needed. Since the traction control light is on as well, I'd take a stab at replacing the rears before the fronts.

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need2no wrote:

Most likely but could also just be wiring on them gone bad.
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Sounds like that's the case.. if they are anything like the 3 series sensors the diagnosis approach to finding out which sensor is responsible for the fault is fairly simple and requires measuring the voltage on the pins of the sensor while the hub is rotated.... I wrote a detailed description for the 3 series E36 car.. it might be applicable for you you can only try I guess? It is a bit tricky but can be done and saves you a packet... So here is my post.. print it and give it a bash..
Firstly, I didn't think all this up myself I used some other posts on the site... one from cotty in particular..
http://www.e36coupe.co.uk/forum/viewtopic.php?t $908&highlights+resistence+resistance
Which can be found there, but I thought I'd write up what I did when my ABS light came on, because I haven't found a complete guide to the repair as of yet on here..
First job is to test the sensors, from what I have read the front sensors tend to go more frequently, so I'd start with those. They are also easier to test. You'll need a voltmeter, very sensitive (milli-volts), you can measure the resistance too, but I found that difficult (see cottys post). Anyway.. remove the front wheel you're looking at, the sensor is located within the wheel hub, but the connector in question is actually located behind a black plastic casing, which is attached to the inside of the wheel arch. One of the front wheels will also have a break pad sensor. Basically trace the cabling from the hub to the plastic cover attached to the back of the wheel arch and open it.. The ABS sensor connector should be grey. The black connector is for the brake pad wear sensor, and we won't need to look at that.
Disconnect the grey connector, the top comes off leaving one half connected to the car electronics (wire leading into engine bay) and the other attached to the sensor... from Cotty's post we're interested in pins 2 and 3 only. Use a small bit of wire and hold them onto pins a and 2 and connect your meter to these. This is fiddly, and be careful not to bend the pins! (I did this on one sensor.. and fortunately for me it turned out to be the one that was duff!) once connected set the voltmeter to milli-volts AC and rotate the hub, the voltage should rise and lower with the hub speed. If is doesn't, my advice is persist a while to see if you have made a mistake with the settings on the meter, or the wires are not in contact with the pins, a little time and effort is a good thing, you'll only have to repeat it later if you're not sure you got the right readings which means more time wasted. Repeat this step for both the front wheels, if you find a duff sensor, my advice is continue to check the others, sometimes more than one fails.
The rear sensors are a little different, again one wheel will have the brake pad sensor, I found mine to be the opposite side to the front. To do the rear sensors, I found jacking the car at the back leaving the wheels on.. to be sufficient (please be careful when jacking the back don't want people with cars dropped on their heads! good idea to use stands and blocks for the front wheels to be secure). I didn't remove either of the rear wheels. The sensor connectors once again are found in a black plastic like case that you can open, one for each side, although for this they are tucked a little further back. Best idea is trace the cables back from the sensors in the hub to find them. Again same procedure, open the plastic covers, and take out the grey connector, and separate it. There are only 2 pins in these sensors, so it makes it easier, connect your voltmeter, same settings to this and (making sure your handbrake is off) rotate the wheels. This is where the jacking of the whole car comes in handy.. I found it hard rotating the hub with the wheels off, with them on you can get more torque on the wheel. Again the voltage reading should increase with the speed of the hub rotation. And again, make sure that you have accurate readings and your wires are secure.. will save time later.. don't want to do this again, it's messy and unpleasant under the back!
By now hopefully one of these sensors will have shown NOT to change voltage when the wheel spins. This is our target, buy a new sensor to replace it from German Swedish French car parts, about 60 quid ish.. In my case it was front right (51+vat), so I can talk you through the changing procedure for the front sensors (which is a 5h1t to get out). Rear I am sure will be similar.
Remove the wheel again, jack nice and securely, I also turn the wheels left.. (for right side) so I can get a better view of the sensor. Remove the allen key bolt that holds the sensor in place. You'll notice on the hub there is a small cab which can be removed with an allen key. This is a cap for the sensor, it lines up directly with it from the front and allows you to insert a rod to use to push the sensor out this way. The sensors fit using what I think is called and "interference fit" which means they are VERY tight to get both in and out... Drilling out the sensor can loosen it but I would try others ideas (I don't know who suggested it but it was not me.. don't want to steal anyone else's thunder) soaking it in WD40 (do NOT get it on your discs!) over night can be a good idea they get pretty stuck in there. Be prepared for a long slog they are horrible to get out. Inserting the sensor is not as hard but is not easy, again the purpose of the interference fit is to jam the sensor in firmly.. which is really what we want from this! once the new sensor is fitted, make sure you replace the cap you removed from the hub, re connect the sensor, making sure the wires are clipped where the previous wires were clipped. I gave my arches a good clean up too while I was in there. Re-fit the wheel and drop the car back down... Go to start, and in theory the ABS light should flicker and go off. In my case the car did not even need to be started or moving....
I hope this helps anyone with ABS problems in future.. If anyone wants to add anything to it or correct anything please do so...
Cheers all...
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Excellent write-up Mr. Read. Very detailed (end-2-end) and dummy-proof. I've had the same problem (ABS indicator) on my 95 318i (126K mi) but opted to live with it, thinking the repair-cost might be prohibitive. Will give it a try. Thanks a bunch !
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Thanks! Just what i was looking for, excellent. Thanks for taking the time, will give that a blast and hopefully will be a bit of a cheaper job than antisipated..... THANKS AGAIN !
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