ABS light on

The ABS light has just started to come on, on my 318 (1998) any ideas?
Fluke

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Defective speed sensor on one of the wheels.

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ABS sensor probably.. I wrote this for a forum I go to.. can help you do the job yourself.. I've also done the rear ones too.. you'll need a drill to drill out the old sensor..
***** POST ***** 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 carefull 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 pastic 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 elses 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...
*** POST END****
Hope it helps...
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the
http://www.e36coupe.co.uk/forum/viewtopic.php?t $908&highlights+resisten ce+resistance
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Thanks for this - will hope to add/return as I check these sensors soon.
Fluke
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It is not normal that one would need a drill to get the sensors out. Let me rephrase that, I took all of my sensors out with out the need for a drill. The sensors are a very snug fit in the hole they go into, and a bit of Liquid Wrench may help to get them free if they are stuck.
Another possibility is that there is trouble with the ABS relay body or solenoid body, or whatever they call it. Look in the engine bay for the thingie that has all of the brake pipes connected to it, this thingie has solenoid operated valves inside. If one or more valves is sticky, the ABS light will come on, which indicates the vehicle's ABS System is disabled.
When you start the car, the ABS light is among the lights that come on during the self-test. It should go out when the engine is started and remain out. If the light comes back on or remains on all of the time AND the vehicle is not moving, then the speed sensors are most likely not part of the trouble, and you need to service the solenoid body -- sometimes you can flush the brake fluid and clear the debris that is clogging the valve(s). If the ABS light goes out after engine start while the vehicle is not moving, but then comes on after the car starts rolling, or comes on randomly as you drive around, then the speed sensors move to the head of the line for things to replace.
Before you do anything, you need to determine what mode the vehicle is in -- moving or stationary -- when the light comes on.
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Jeff Strickland wrote:

and if its not the sensors, and it ends up being the ABS/ASC module, there are two ways to get it. you can get the whole unit which is over 1,000 bucks i think, or you can just get the repair kit which is a new control unit section of the module, without the hydraulic portion. there are torx screws that hold it on, its easier, cheaper, and you wont have to do a bleeding procedure either (which needs to be done with a BMW DIS tester hooked up)
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I'm not sure I made it clear, but the ABS system talks to the Diagnostic Port, so one need only visit an independent BMW service center to plug into the diagnostics and find out what the car thinks it is unhappy about.
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I've had some good ideas from you and the other posters here, the cars my gaffa's - he is going to sell but he wants the light out before hand. Ive told him I'm doing no dodgy stuff, I also explained him to be certain he would need to take it to a BMW service centre. Thanks again Fluke.
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Just going through this myself.. here's my dramas so far.. car is new to us (though was born in 95) and sure enough the ABS lamp came on within minutes of us owning it..
The light comes on as soon as the ignition is turned - I pray to the god of ABS pumps and offer some skin off my knuckes and a set of multimeter leads trying to measure just one of the 4 sensors (yep that one was OK) It started raining heavily and the missus needed the car so I have to abandon play
Decided to just get the brain read and have done with it...20 lighter but at least I know its the front drivers side sensor that's gone
order a new sensor (70 lighter - but at least I will know what ABS feels like and will extinguish the lamp on the dash!)
took wheel off, took sensor connector from its plastic housing and put new leads across pins....bingo the brain reading seems to be telling the truth - 0 ohms - open circuit
decided to get a new "L shaped" allen key (ever the optimist) and tapped it into the sensor bolt head put some release fluid on there - tapped it a few more times to try and get the fluid in there - went and had a cup of tea and degreased my hands went to the allen key, gingerly put pressure on, no loud snap - just a soft chewy tear - more lost skin from knuckles, head still attached to allen key - end of thread still in sensor/hub, DOH!
Ok get mole grips and gently twist sensor body, rocking it back and forth whist using a pulling motion it eventually came out,without any real dramas compared it to new sensor - and its a different design,,,,,,
Old one has a chromed metal body and 2 pins in connector - and an earth wire from chassis body to sensor body New one is made from black plastic (ok so it won't seize if you don't put coppaslip or whatever in there) - but it also has 3 pins in the connector
Put wheel back on sulked for a while...
Tomorrow I'm giving car back to the garage where I bought the new sensor and getting them to drill the remains of the bolt out and fit a replacement sensor as I really couldn't face trying to get the brake disk (rotor) allen bolt out to try and get to the back of the sensor bolt to have a go at drilling it and chasing the thread myself - not that I have the correct sensor to refit anyway...besides I have lost enough skin for one week on this car (I knew it wasn't going to be a 10 minute job - they never are) I never expected it to be a three figure ammount to extinguish the bulb
On the bright side it means I get to drive my kit car (lotus 7 clone) to work tomorrow for the last time on standard carbs hoping to loose some more skin fitting a set of motorcycle carbs to it on Thursday :-) Had the bolts in and out so many times I know they won't cause any dramas replacing them
pray for good weather tomorrow -as it has no windscreen or roof I will be offering a sacrifice to the skin gods for Thursday's encounter and be taking waterproofs to work
I think the moral of the story is getting someone else to do a job you are really not geared up for - is really much cheaper,easier and quicker in the long run
I wish I had the gear to read the brain, a decent set of allen key sockets, a ramp, a garage blah blah - but I don't, so will have to do more overtime
Regards Rob
"You can't have everything....where would you keep it?" Steven Wright
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I've just changed all the discs on my '97, and they all came out easily. As they did the last time - although I do use a smear of copper grease on them
--
*Middle age is when it takes longer to rest than to get tired.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Impact screwdriver works wonders on those. Got one for 14 quid in Halfords many years ago, always works ;-)
--
Who needs a life when you've got Unix? :-)
Email: snipped-for-privacy@unixnerd.demon.co.uk, John G.Burns B.Eng, Bonny Scotland
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One of the latest things in boy's toys is a cordless impact drill/driver. Not to be confused with a hammer drill. Wonderful things. They're a bit expensive at the moment but sure to come down in price.
However, there's no reason for that grub screw to be tight - it does near nothing, after all.
--
*Not all men are annoying. Some are dead.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I have seen the 12v impact drivers and wondered if they would be any good (eg powerful enough to remove the bolts after garages have abused them with windy guns..)
On my other car (the seven clone) - the grub screws that hold the disks in place have been omitted completely, as the layer of crust that accumulates shortly after fitting them is more than enough to keep them in place when changing a wheel - and a torque wrench is the right tool to put the nuts back on with
Well its been a really good day for me, it didn't rain (in fact it was really mild for the time of year and we had sunshine)so the journey to and from work was great in the seven
The BM got dropped back off tonight- they drilled the bolt out - fitted the new sensor - the ABS light is now off when the engine is running The total bill came to .... 25 !!!! yes I didn't mistype that 25 (why did I even bother getting my hands dirty with this job ??!!!) I will be using this garage more often in the future - just a small local one tucked down a back street
managed to round the evening off by removing the single downdraught from the seven and fitted the bike carbs - very happy bunny as they ran first time!!!! albeit a bit rough as they aren't balanced yet Not even mild grazing of the knuckles Just got to sort out a throttle cable and richen the mixture up a little and were in business :-)
Regards Rob
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