ABS

[Andy335Touring]

My ABS light stays on all the time with the ignition on, it's been like it for i guess around two months but my MOT is due.

The first thing i spotted was one of the sensor wires had rubbed through to the wire so i got this replaced but it wasn't the fault.

After searching the tech sections old posts on the subject it doesn't sound like a sensor or sensor wiring fault.

It's more pointing to the ABS ECU or one of the three(???) relays ?

All i've done tonight is to pull the two relays off on top of the pump to check for dirty/rusty connections, i've also checked the C101(?) plug on the bulk head as theres a trigger wire for the ABS runs through it but all the connections look clean.

In the fallowing post some one says theres a relay on top of the ECU above the glove box but i've taken the ECU off and i can't find it ? Is this a pre/post face lift change ?

When i bought my 325 sport the light didnt work so i took out my clocks and found the bulb was missing , replaced the bulb only to find the light stayed on . In the end the fault was with a relay in the glovebox just above the silver control box

Behind the glove box theres three relays, two Orange ones together and one Blue one. Is one of these for the ABS ?



This is from the ETK, it looks like theres a relay above the ECU, i guess i need to have a look in the day light, god i hate these dark nights !

http://img406.imageshack.us/img406/8023/relays1vq5.jpg

I'm leaning towards a fried ECU or relay because like a pratt i vaguely remember shorting a spanner on one of the big Positive connections on the starter motor but i can't remember if the ABS fault started at the same time or not ?

I've read that jump starting can start these kind of problems off due to a spike or jolt of electricity i guess ?

Is there a built in fuse inside the ECU or relays ?

Not that i can get inside of the ECU any way because it's got funny shaped security screws

Oh, well MOT first thing tomorrow, i'm going to volenteer(sp?) to sit in the car and operate the lights/brakes/steering/ect for him to see if i can get away with it, even if i do i want fix it any way.

[Jon_Bmw]

Andy, can't help you, but if you get up early enough. Re-wire the abs light to the engine oil light i think. This will get you your pass and free up some time so that you can do it once you have enough spare time.

HTH

Jon

[Andy335Touring]

cheers mate, i know this bodge

[aus325]

I'm still persisting with my permanent ABS light...

I think Brianmooore mentioned once that he has a car (or 2) that don't have the relay above the ABS ECU.. I do, and this relay does have a fusible link which can easily be repaired. Apparantly this link can go if the car is jump-started, or if jumper cables are accidently put on back-to-front.

However, I have fitted new relay above the ECU, new relays on the pump unit itself, AND a known good ECU, but I STILL have permanent ABS light from turn of key.

I just give up. Good luck with yours...

[Martinaston]

Did you check the plug on the top of the abs pump ? I've never come across a rusted one yet but you never know.
You mentioned you read the other threads but didn't say if you checked the resistance of the wheels sensors, that seems to be the most common problem. May be worth checking the plugs for corrosion and the rings on the hubs are clean and intact.

[Andy335Touring]

I just give up. Good luck with yours...

Cheers Aus, what you say about the relay was afirmed(sp?) by some more research on some of the US forums which i've copied from below.

I wonder if you have some sort of short some where in your ABS wiring to cause that relay to blow as soon as you turn the key ?

Incorrect Jump Starting

If one incorrectly reverses the connections (even momentarily), a relay attached near the top ABS control unit which is located under the dash, left of the steering wheel will get toasted. Discount parts vendors sell this for approximately $21.
This all started a while back when my ABS overvoltage relay fried its little fuse. I replaced it and then about 3 months later it went out again. I replaced it yet again and about 2 days after replacing it, the ABS light pops on again.

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Well If your relay is the metal case type, then all you have to do is gently take the case off and there's a small gauge wire (not a real fuse) on the side, just resolder a similar gauge wire in it's place. I've done it twice. This may sound stupid to others, but what caused it was the relay wasn't clipped securely either time, and bumped the metal case under it, blowing the fuse. Now that I've got it securely fastened it hasn't blown or thrown on the light once.

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91 model year doesnt have that relay. They quit doing that in 89 or so.

That last quote is interesting because my car's an '89.

Well for the MOT i pulled the warning light bulb, he either didn't notice or chose to ignore it.

What it did fail on is the CO2 which is(touch wood) down to a leak i've got on my exhaust, i tried useing exhaust paste but it didn't work so i ordered the proper M3 seals which i couldn't get in time for the MOT.

[Andy335Touring]

Did you check the plug on the top of the abs pump ? I've never come across a rusted one yet but you never know.
You mentioned you read the other threads but didn't say if you checked the resistance of the wheels sensors, that seems to be the most common problem. May be worth checking the plugs for corrosion and the rings on the hubs are clean and intact.

No, i didn't check the plug but i should have whilst i had the cover off

My understanding is by reading what Brian says is if it's a sensor problem the light will go out but then come on when you move above 5mph ?

I've had the front sensor plugs apart and they were clean, but i will have a closer look into the sensors and there wiring.

[Martinaston]

They should be about 1k ohm if you check the resistance but willl vary a tiny bit on each. From what i can remember of the system i removed it didn't have a relay near the abs ecu there located on the pump.
If you follow the ecu plug back it should have 3 or 4 wires going into the accesories plug and then just continue through the bulkhead because its a seperate loom from the others.