ABS Problem

[jibbers]

Took the car for a spin and managed to lock the wheels up , me thinks this should not happen as i have ABS , i looked at warning light and not on , just stripped and found the usual trick .... No bulb in it !
Does anybody know how i can find the fault , is there a way of testing the sensors on wheels , or if the relays on the ABS unit itself are a common problem ?
Also if anyone has bought sensors or relays in the past can you let me know how much you paid for them , i tried BMW parts dept and they shut at 12 on a saturday , this dont figure, surely most people only have weekends to fix their cars ! ! ! SORT IT BMW !

Cheers Jibbers

[Brianmoooore]

First, put the bulb back in and see what happens. Light should come on with ignition and then go out when engine is started..
If it goes out as normal, and stays out untill you reach a speed of about 5 MPH, then the problem is with the sensors. Check that the sensor plug and sockets are not corroded, and that the sensor toothed wheels at the hubs are not gunged up.
You can check the sensor outputs with an AC millivoltmeter, or better, an oscilliscope. At the same road speed, you should get similar signals from each sensor.

[jibbers]

Hi Bri !
Have got bulb workin as it should , it goes out when engine is started but as soon as i brake for the first time the light comes on and stays on , im not really sure on how to do the test you described so i think my first task will be to clean up the hubs and check all connections are ok, if that dont work i will find a willing person to swap parts with until i get a result cos i aint payin the prices i just looked at on RealOEM.COM.....FOOK..!.!.

Cheers Jibbers

[Brianmoooore]

You can check the DC resistance of each sensor with a multimeter fairly easily, to see if they are all the same, but the actual sensors are fairly reliable unless they are physically damaged. Toothed wheels and connectors are the usual culprits.
If you do have to remove a sensor, you may find that it has taken root, and doesn't want to come out. Good soak in WD40 required.

[jibbers]

Cheers my man i will give it a go in mornin , what setting do i need to put my meter on and at what point do i test it , the wiring to the sensor or the sensor when its off the car ? In case you have not noticed im a bit of a drongo when it comes to electrics ! !
I have also taken note that the ABS unit itself has 2 relays in it , are these a cause for concern ?
And the control unit has one too , is this a concern ? , and do you know where it is situated ?

Jibbers

[Jon_Bmw]

Exactly what brian said basically, i had the exact same problem, well minus the missing bulb. To take a resistance reading of the front sensors unplug the yellow conector in the engine bay, check the resistance on it by putting your electrodes in the two holes effectively. They should be the same both sides, if not you know you've got a problem.

I can't remember if high of low resistance means a good of bad sensor, search for it on the net i'm sure you'll find it.

If its a problem with the rear,don't ask me as i have't had a problem with that i'm afraid.

[Martinaston]

The rear sensors have connectors under the back seat, But if your checking them for AC current i assume you need them still connected to the control unit?

[Brianmoooore]

No, they are small AC generators. Connect the sensors directly to a AC millivoltmeter or scope. You're looking for identical signals from each sensor under the same conditions.

[Brianmoooore]

Just re read Jibbers second post, and I think we may be on the wrong track.
The ABS sensors are continuously monitored by the ABS brain, and the ABS warning light will come on as soon as you exceed 5MPH, not when you brake for the first time.

ABS control unit looks like the engine ECU and lives above the glove box. The motor/valve assembly is behind the LH headlamps with ABS written on it's plastic cover in big letters.

[jibbers]

Right have at last got onto car , have got both yellow connecters out but i cant seem to get any reading off either , i have got my meter set to 200 ohms is this correct ? [im a spoon ]
Jibbers

[jibbers]

your right it does come on when i hit 5 mph and not the braking as i first thought , are you any wiser ? Jibbers

[Brianmoooore]

Can't remember and it's not in my notes. Giveme tenmoinutes and I'll measure one.

[Brianmoooore]

990 ohms on one car, 975 ohms on another.

[jibbers]

Reckon you hit the nail on the head there my man ! ! !

1000 on one side .... 0 on the other !

Thanks Brianmooooooooooooooore , and everybody else that gave a bit of input , some robber would have shafted me for that ! !

I will seek a new sesor the moro and post my result here , so do check it out cos who knows , i may need you all again if it dont work !

Thanks again Jibbers

[Brianmoooore]

You mean zero ohms or infinity? If zero, then check the cable to the sensor for damage. You may be able to repair it.

[jibbers]

Zero ohms or infinity ?
Soz chap i only speak my native moron tongue !



The meter said 0 so i assumed the sensor was fooked , i will have a look before i buy one , if i can sort it out i will ....

Cheers Jibbers

[Brianmoooore]

The sensor consists of a coil of very fine copper wire. Since no power is applied to the coil, it's unlikely to have melted into a solid lump. What usually occurs is a break in the wire, which would give infinity on your meter.
For the two wires to be shorted together (zero ohms), I would think this is most likely in the connecting lead, where the two wires have become exposed and twisted together. May be (probably) wrong, but worth a check.

[jibbers]

CHECK CHAT

[Brianmoooore]

Pardon?

[jibbers]

Thanks Brianmoooore the prob is all sorted now , it turned out to be breaks in the wire , it was totally rotten , i just cut a new piece of wire in and now i have fully operational ABS .

Thanks again Jibbers

[Brianmoooore]

You're a few pennies better off today , than you thought you were going to be last Saturday, aren't you? Glad it's all sorted.