ABS Problem Has Everyone Stumped!

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DougieN13
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Mon Sep 28, 2009 2:38 pm

The ABS light has been on my F Reg 325i for the past year since i bought it.

When i test drove the car the light wasnt on and then when i cam e back to buy it the light was on and the guy said was because he'd left the lights on and when they jump started the car it came one.

I hadnt fixed it till was time for my MOT as i wasnt that bothered about having ABS but needed it to be working to pass an MOT

We first tried changing the relays to see if they had broken but no luck, tried few things then as i was in a rush i though sod it il just take it to a garage and get them to fix it and bite the bullet on the price.


They have had my car 3 weeks now and still havnt been able to fix it, i went in at the weekend to see what they have tried because i thought they were being a bit slack or milking it but he got the wiring diagram out for the abs system in and started going through all the bits they've checked and replaced.

So far they have checked al the sensors by the wheels
Swapped the ABS ECU
Replaces the ABS pump
checked all the wiring and points

Yet still the bloody light is staying on

The only problem they have found is (bare with me as i didnt understand 100% what they were saying)

on the bit of the ecu that links with the ignition, they said there should be a signal sent down from the ignition down to the ECU and then a signal sent back up which then turns the light off but there is no signal coming back, so they are thinking its still an ECU problem, but im pretty sure the ECU i bought to replace the old one was working as i bought it of a very reputable place.


Has anyone had any similar ABS problems or have any suggestions of things to try?
DougieN13
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Mon Sep 28, 2009 3:08 pm

Heres a wiring diagram of the abs system for my car and iv put a selection around where the signal problem is i tried to describe
Click below to see
http://www.bigdealclothing.co.uk/abs.html
GeoffBob
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Mon Sep 28, 2009 4:43 pm

Yeh OK, I get what he was trying to tell you. Looking at your diagram, the block marked "solid state" in the bottom left is the "brains" of your ABS. Your ignition gives it power when the car is running and the "brains" turns the ABS light "on" via the ABS indicator control (at pin 29).

The reason it's doing this is because you genuinely have an ABS fault that is being communcated to the solid state "brain" from your electromechanical ABS solenoid block (the bulky thing under the bonnet that interrupts/controls the supply of fluid to the brakes).

My suggestion is that you check the main fuse that supplies power to the ABS solenoid block. Not the 7.5A fuse that goes to the ABS "brain" - but the one goes to the solenoid block! This is the most common cause of ABS failure and the light coming on. As far as I recall you find this fuse elsewhere under the bonnet, not with the other fuses in the box (I could be wrong, I'll have to look it up). I am sure someone else will be able to tell you where to find it.

Hope you come right Dougie,

Regards
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DougieN13
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Mon Sep 28, 2009 5:36 pm

Thanks Geoff

Il check that fuse out and hopefully will fix the problem

Will let you know, if you find where the fuse is will you let me know, save me searching aroung ha

Dougie
suzie650
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Mon Sep 28, 2009 6:52 pm

What year is the car?
DougieN13
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Mon Sep 28, 2009 7:29 pm

suzie650 wrote:What year is the car?
1988 i think, its an F Reg
suzie650
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Mon Sep 28, 2009 11:26 pm

Did they check the overvoltage protection relay that on a lhd is next to the steering column? (I suppose it has to be somewhere behind the glovebox on rhd cars)
This relay has a fusible link and has been described many times as a prime suspect for such a fault by a few knowledgeable people on here.
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Brianmoooore
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Tue Sep 29, 2009 12:35 am

What suzie said!
If they've only found the two relays in the ABS pump housing, they haven't found the correct one!
GeoffBob
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Tue Sep 29, 2009 9:56 am

suzie650 wrote:This relay has a fusible link ...
That's the one Dougie :thumb: . Sorry I couldn't tell you where to find it. I do however seem to recall that jump-starting the car has an awful habit of blowing that fuse, so I do believe that finding the overvoltage relay and the assocuated fuse Suzie described will solve your problem.
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DougieN13
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Tue Sep 29, 2009 10:25 am

You lot were right

The wiring in that relay was dodgy, and the garage hadnt checked that one as was not directly involved with the ABS on the diagram.

Thanks for all your help

Now i can can get my beaut back on the road!
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Brianmoooore
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Tue Sep 29, 2009 10:39 am

I hope you haven't paid these muppets any great amount for their incompetence!! This is a very basic and easy fault to diagnose, and the relevant wiring is plainly shown on the circuit diagram.
DougieN13
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Tue Sep 29, 2009 3:15 pm

Yeah im not planning on paying them much.

This is the one time iv decided to use a garage rather than do it myself with a friend because i thought would be easyier and quicker.

Well i know better next time ha
DougieN13
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Wed Sep 30, 2009 10:54 am

Brianmoooore wrote:I hope you haven't paid these muppets any great amount for their incompetence!! This is a very basic and easy fault to diagnose, and the relevant wiring is plainly shown on the circuit diagram.

Oh and guess what

Picked up my car from the garage this morning and driving back realized the rev counter and the computer isnt working now.

So you take it to a garage to fix a problem and by fixing one they create two more.

Awesome.
daimlerman
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Wed Sep 30, 2009 11:36 am

I have a zoner local to me with the same issue.
We have swapped the relay mentioned for the same one in my touring without success...
As this car is also displaying all the faults that I would expect from an SI board failure we have swapped the cluster as well,still an ABS light when moving,no rev counter and no MPG meter....
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GeoffBob
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Wed Sep 30, 2009 11:36 am

Sorry to hear this Dougie. If it's any consolation I am sure that we have all had experiences like just like this.
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Wed Sep 30, 2009 1:23 pm

I've had a non working revcounter in the old ix I'm putting back together - found out that the C101 was totally messed up with non matching pins -> no signal.
Although this is ruled out if it happened on a previously known working car.
DougieN13
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Wed Sep 30, 2009 1:59 pm

mmmm yeah im not sure

Havnt had a good chance to have a look since picked it up as had to go straight to work, will have a look tonight.

Im hoping they have just missed something when putting it back together
DougieN13
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Wed Sep 30, 2009 2:23 pm

daimlerman wrote:I have a zoner local to me with the same issue.
We have swapped the relay mentioned for the same one in my touring without success...
As this car is also displaying all the faults that I would expect from an SI board failure we have swapped the cluster as well,still an ABS light when moving,no rev counter and no MPG meter....
mmm i know someone else with the same problem, must be very a common fault
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westie84
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Wed Sep 30, 2009 7:38 pm

DougieN13 wrote:
daimlerman wrote:I have a zoner local to me with the same issue.
We have swapped the relay mentioned for the same one in my touring without success...
As this car is also displaying all the faults that I would expect from an SI board failure we have swapped the cluster as well,still an ABS light when moving,no rev counter and no MPG meter....
mmm i know someone else with the same problem, must be very a common fault
Hi im the zoner with the same problem.
I have changed a sensor that was split and have checked all sensors with a multimetre and they are all reading the same. I have cleaned up the front ABS pick up teeth they are like new now, the rears are fine. I swapped the relevent relays with known working ones and still no luck. I dont know what else there is to try other than a fault in the wiring between the ABS sensors and ABS ecu but the light only comes on once the car gets moving which would suggest a wheel speed sensor problem?
Also the rev counter and mpg have just stopped working, someone suggested the batteries in the back of the cluster may have leaked acid and messed up the circuit board, i have check this and all seems ok. I have also borrowed a cluster from daimlerman but still had the same problems :?
Can anyone help?
GeoffBob
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Wed Sep 30, 2009 8:43 pm

I could be way off beam on this one but its worth a try. I seem to recall the ABS unit also reads the cars speed from the "taximeter" output of the speedometer. If that fails the mpg stops working and the ABS shows a warning when the vehicle starts moving (both due to the absence of the speed signal). Check the back of your speedo, it has six pins on it. Pin 3, next to the +12V supply, is the taximeter output which feeds to the mpg and, I think, also to the ABS. Check this to see if it runs to the ABS and is intact.

Also, do you have same diameter tyres front and back? I have seen ABS computers show up warning lights if the computer is unable to reconcile the ABS signals from the front with the back (because it thinks the wheels are turning at disimilar speeds due to different size tyres).

I apologise if I am wasting your time, but its been a while since I worked on an E30 ABS. If any of this rings a bell with anyone else I am sure they will pick up on it and guide you closer to a solution.
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Brianmoooore
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Wed Sep 30, 2009 9:43 pm

GeoffBob wrote:I could be way off beam on this one but its worth a try. I seem to recall the ABS unit also reads the cars speed from the "taximeter" output of the speedometer. If that fails the mpg stops working and the ABS shows a warning when the vehicle starts moving (both due to the absence of the speed signal). Check the back of your speedo, it has six pins on it. Pin 3, next to the +12V supply, is the taximeter output which feeds to the mpg and, I think, also to the ABS. Check this to see if it runs to the ABS and is intact.
I'm afraid you are way off beam! The ABS does need a road speed input, but it gets this by processing the signal from its own wheel sensors, not from the speedo circuit.
daimlerman
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Wed Sep 30, 2009 9:50 pm

All of these issues seem to relate,likle westie84's problems,to pre-facelift ABS,I can see no other common thread.Now my ABS in my early(88) touring has a silver relay;
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westie84 has a black plastic relay...but....swapping the relay's gave the same indicators,ie,my touring behaved normaly,gave two flashes of the ABS light,westie's car gave no light until he reached 10mph.....on this basis we ruled out the relay,as his light only plays up when moving, this points toward a sensor problem,but all sensors show around 1000 ohms on test,he's polished the sensor rings so we have ruled out dirt interfearing with the pulse signal,so what have we missed? :cry:
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Brianmoooore
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Wed Sep 30, 2009 10:06 pm

DougieN13 wrote:Picked up my car from the garage this morning and driving back realized the rev counter and the computer isnt working now.

So you take it to a garage to fix a problem and by fixing one they create two more.

Awesome.
This can be a by product of the main car battery being disconnected for a while while they were working on the car - the SI board batteries could have just been clinging on to life, and have now given up after their charging supply was removed.
Then again, it could just be another c*ck up!
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westie84
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Thu Oct 01, 2009 12:59 am

Brianmoooore wrote:
DougieN13 wrote:Picked up my car from the garage this morning and driving back realized the rev counter and the computer isnt working now.

So you take it to a garage to fix a problem and by fixing one they create two more.

Awesome.
This can be a by product of the main car battery being disconnected for a while while they were working on the car - the SI board batteries could have just been clinging on to life, and have now given up after their charging supply was removed.
Then again, it could just be another c*ck up!
My car has been in storage for nearly a year with the battery disconnected, the battery was fully charged two weeks ago and the car has been used almost every other day sinse.
Could this have nackered the batteries in the si board causing the rev counter and mpg to fail? :?
DougieN13
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Thu Oct 01, 2009 10:34 am

Brianmoooore wrote:
DougieN13 wrote:Picked up my car from the garage this morning and driving back realized the rev counter and the computer isnt working now.

So you take it to a garage to fix a problem and by fixing one they create two more.

Awesome.
This can be a by product of the main car battery being disconnected for a while while they were working on the car - the SI board batteries could have just been clinging on to life, and have now given up after their charging supply was removed.
Then again, it could just be another c*ck up!

Thanks mate

Well iv took it too the garage and told them to fix it as it was working when i brought it in so will be free of charge.

But i will pass on the information as they dont seem to be that great.

Where are the SI batteries located?

Dougie
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Thu Oct 01, 2009 11:12 am

willnz wrote:SI batteries are inside the instrument cluster. Arrowed in the pic below..

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Thanks mate your a star!
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westie84
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Thu Oct 01, 2009 11:45 pm

Tonight i have checked the output of my si board batteries, they seem fine giving a reading of 2.5v. What else could be the cause of my rev counter and mpg to suddenly stop working? :?
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westie84
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Thu Oct 01, 2009 11:52 pm

daimlerman wrote:All of these issues seem to relate,likle westie84's problems,to pre-facelift ABS,I can see no other common thread.Now my ABS in my early(88) touring has a silver relay;
Image
westie84 has a black plastic relay...but....swapping the relay's gave the same indicators,ie,my touring behaved normaly,gave two flashes of the ABS light,westie's car gave no light until he reached 10mph.....on this basis we ruled out the relay,as his light only plays up when moving, this points toward a sensor problem,but all sensors show around 1000 ohms on test,he's polished the sensor rings so we have ruled out dirt interfearing with the pulse signal,so what have we missed? :cry:

Any ideas folks? :banghead:
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Brianmoooore
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Fri Oct 02, 2009 12:12 am

The 1000 ohm test can only prove a sensor is dud if it doesn't pass. Passing doesn't necessarily mean its good!
Ideally you need to monitor the outputs of the wheel sensors with an oscilloscope, with the wheels turning, put you may get meaningful results by connecting an AC millivoltmeter to the sensors instead.
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westie84
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Fri Oct 02, 2009 12:27 am

When testing with the millivoltmeter, do the wheels need to be turning?

Thanks
Dave
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Brianmoooore
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Fri Oct 02, 2009 9:41 am

westie84 wrote:When testing with the millivoltmeter, do the wheels need to be turning?

Thanks
Dave
Yes.
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