ABS - quick second opinion please!

[simon-york]

I would appreciate someone else's thoughts on this if you will...

Earlier this year I took out my instrument cluster and found the ABS warning light bulb missing. "Oh yes, I thought, someone has taken this out to pass the MOT" (official inspection here in the UK). Sure enough, although the light went out once the engine started, it came on again as soon as the car moved forwards - or within a second or two. Everyone says that the ABS system should be ok, but that at least one sensor had gone - or was maybe clogged.

My mechanic agreed with this, but said he did not have the equipment required to check the system, and to go to the dealer for them to check it. Well, I have been busy doing other things so I have not done it and the annual MOT inspection is now due. So, I have tried something which I hope will prove a useful alternative and maybe help others.

My idea was if one of the sensors returns a fault as soon as the car rolls forwards, I would simulate this by jacking up the car and spinning one wheel at a time. Sure enough the offside front wheel turned on the warning light straight away - the nearside did not. I have not tried the rear wheels since I appear to have at least one faulty one. On this basis I am going to order a new offside sensor tomorrow.

What do other members think? Worth a try? Thanks in advance for your thoughts.

Simon Daubeney, York, England. 1989 530i SE M30 5 spd Bilsteins Alpinas

[tim]

wasn't there something about the seatbelt buckle mechanism?- there was a sensor or something that went bad and wasn't worth replacing- thus the many cars out there that have their abs lights removed.

My memory is failing here, but perhaps it's an avenue you can explore if the new sensor doesn't clear things up. It would also be instructive to run the codes-although you needn't go to a dealer.

[tim]

wasn't there something about the seatbelt buckle mechanism?- there was a sensor or something that went bad and wasn't worth replacing- thus the many cars out there that have their abs lights removed.

I take that back- I'm thinking of the SRS light. Sorry. Nothing to see here. Move along. Just a guy who smoked out too many brain cells.

[winfred]

if you have access to a lab scope you can read the waveform from the sensor, or with a regular multimeter you can read the ac voltage when you spin the wheel

[simon-york]

if you have access to a lab scope you can read the waveform from the sensor, or with a regular multimeter you can read the ac voltage when you spin the wheel

Thanks for that, but I have run out of time really. Given that one wheel turned the fault light on and the other didn't, it is surely likely that the offside sensor is faulty?

Simon Daubeney

[tim]

Yes, but wasn't that the diagnosis anyway?

Either an obstructed lens or a faulty sensor.

Have you looked at the diagram on the ETK?

http://rust.mine.nu/bmw/

Put it in a skid to see if the ABS pulses?

[ron525]

I would say you need the "nearside" sensor. Since the "offside" sensor reacted to that wheel spinning, while all other wheels are standing still, that sensor works. The "nearside" one is not working since nothing happened when you spun that wheel.

[632 Regal]

go, rippin it up, in a field, and try to lock the brakes, the tire that skids should be the offender. easier than checking manually and pretty much a guarantee to find the correct one.

[winfred]

one dies they are all shut down

go, rippin it up, in a field, and try to lock the brakes, the tire that skids should be the offender. easier than checking manually and pretty much a guarantee to find the correct one.

[Bellicose Right Winger]

Ditto on the "nearside" wheel/sensor. Perhaps you can check this by spinning the rear wheels. If the light comes on, and I think it will, because ABS ECU is seeing only (1) speed signal and it's expecting (4), this will confirm nearside.

After you locate the the wheel, make sure the slots in the chopper wheel behind the rotor aren't filles with rust and scale.

Paul Shovestul

I would say you need the "nearside" sensor. Since the "offside" sensor reacted to that wheel spinning, while all other wheels are standing still, that sensor works. The "nearside" one is not working since nothing happened when you spun that wheel.