Author Topic: Integral ABS - CAN (servo brakes) "Pressure in rear/front circuit too low"  (Read 65831 times)

kobus

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Symptom:
ABS Light on, only residual braking left

Solution:
Try the following in order:

  • Bleed it.
  • Check for resistance in the front/rear sensor line.
  • Check handbrake/footbrake light switch adjustment.
  • Replace the ABS unit  :'(

Do a sensor drift test.
If you get an error: "Offset values of internal pressure sensors not OK" it usually means you have to replace the control unit because the sensors stopped working.

Prevention:
Properly bleed the brakes every year and use the ABS bleed test to move the fluid in the ABS module itself to prevent corrosion and damage of the sensors.
Do not use a high pressure cleaner!
« Last Edit: April 19, 2013, 09:20:20 AM by kobus »
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Jughead

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A possible fix for this problem

These are your 2 pressure relief valves, the Yellow for the front and Red for the rear circuits.


Sometimes these valves get stuck, thus not allowing the pressure to release. 

Firstly remove the rubber boot around the base of the valve.  They are rather tight and will need a little force to get them off.  They are rubber however so will come off without damage.


Next, remove the valve itself, using a 26mm wrench.  This is what it looks like.


Make sure that the plunger on the end travels up and down freely, without getting stuck.  It is spring loaded with a rather heavy spring, but you should be able to depress it against the spring pressure by hand.


This is the movement you should have.


Push the plunger in a good few times to make sure it is moving smoothly.  Replace it, bleed the pump (in the correct sequence) and wheel circuits and test again.  You can even swap the 2 valves around to see whether the problem shifts to the front wheel.

I have had a number of problems with pressure and have been able to resolve most of them doing the above.  If the problem persists and moves if you swap the valves, then the valve will need to be replaced.  Unfortunately, BMW does not sell the valve loose so you will have to source those elsewhere.

Hope this helps!

kobus

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Wow, thanks for this. It will help a lot of people!
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... and then the company fleet.

StephanT

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and another Karma applaud for Jughead!

+1

Alexm1

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Jughead, thanks, I hope I won't need this but a clear and concise process if I do. Much appreciated.
Alex

Jughead

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Pleasure!

Mission

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I have the iABS on my 2004 K1200RS and as Jughead suggested my problem may have been the pressure relief valves but alais it was not the fix. As I have tried every other fix,  I am now back to my original suspect, the sensors ( Not the wheel speed sensors ) which are 5 volt peizo ceramic transducers under the bottom of the pump unit which drive Mosfets for front and back systems. I originally had the "rear brake circuit pressure high " and 4Hz light but now it completely random and sometimes I have both lights flashing with or without brakes. 

Does anyone know if Module Master in America does the iABS overhaul yet ?

Jim

Alexm1

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Jim, I understand MM will be ready later this year. There is another repairer in Tennessee, automotive Scientific Inc.
What about jughead, does he fix to that level?
Refer to this note in I BMW.
http://www.i-bmw.com/showthread.php?t=44589
Alex.
Alex

Jughead

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What about jughead, does he fix to that level?
Refer to this note in I BMW.
http://www.i-bmw.com/showthread.php?t=44589
Alex.

I have honestly never had need to repair one of these pumps as they, to my mind anyway, are the better pumps to have.

I do, however, have a spare one which was given to me some time back.  I do believe that it was also replaced when it went "Faulty", but that the fault was eventually traced down to a chafed wiring harness.

I will have a look over the weekend and see what dismantling it entails.  I have also seen a huge sludge buildup in some of these pumps despite the fluid being flushed regularly.

Will report back in due course.
« Last Edit: August 19, 2013, 12:31:17 PM by Jughead »

Jughead

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OK, I have been fishing around while refurbishing my spare ABS pump.

Looked like this:



Now looks like this after the strip and clean:







While I was at it I came accross this sensor:



Made by FTE, it is a pressure transducer, and no doubt the part that results in the Pressure Errors within the pump.

Outside looks like this when removed:



Inside looks like this:



I am at present trying to source these to test with.
« Last Edit: August 19, 2013, 06:54:30 PM by Jughead »

bikecrazy5

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brilliant work jughead :D

Beamietoo

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Re: Integral ABS - CAN (servo brakes) "Pressure in rear/front circuit too low"
« Reply #11 on: October 14, 2013, 03:42:33 PM »
@ Jughead,

I have see a lot of abs control modules and can say that yours is even cleaner than a new unit !
Curious what you use to achieve that result?
Diapers and politicians should be changed often.

Jughead

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Re: Integral ABS - CAN (servo brakes) "Pressure in rear/front circuit too low"
« Reply #12 on: October 14, 2013, 04:03:55 PM »
Bead Blasted!  ;D

Beamietoo

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Re: Integral ABS - CAN (servo brakes) "Pressure in rear/front circuit too low"
« Reply #13 on: October 14, 2013, 04:14:46 PM »
NICE !!
Diapers and politicians should be changed often.

Kishon

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Hello everyone! I am a motorcyclist from Poland and have 2005 BMW R850R. My integral ABS just break up. I am looking for information that could help me in the repair. I see that Jughead has done a great job with his pump. I'm interested in, is there a way to check this pressure transducer? Is it possible to measure the electrical resistance in order to check and, if so, does anyone know the correct value? Thanks for any help!