ABS and accelerometers
04-21-2009, 01:20 PM
#1
Three Wheelin'
Thread Starter
ABS and accelerometers
As a follow-on from my PDAS bleeding issues, I've just had a call from the shop to tell me that my ABS problems (i.e. not working) are due to the failure of both accelerometers (it's a C4).
Quite apart from the fact that these items are currently quoted at £1200 each I'd like to get some opinions as to how realistic this diagnosis might be.
Apart from the obvious potential problems of physically "jamming" through internal debris has anyone any idea how else these ludicrously expensive items can "fail"?
I'm reluctant to attempt to source used replacements unless I can prove they really are faulty.
Any ideas??
Regards
Dave
Quite apart from the fact that these items are currently quoted at £1200 each I'd like to get some opinions as to how realistic this diagnosis might be.
Apart from the obvious potential problems of physically "jamming" through internal debris has anyone any idea how else these ludicrously expensive items can "fail"?
I'm reluctant to attempt to source used replacements unless I can prove they really are faulty.
Any ideas??
Regards
Dave
04-21-2009, 01:58 PM
#3
Dave,
Here are the specs from the Shop Manual for testing the sensors:
If they don't meet spec you should open them up and see if they can be cleaned. I've seen several posts about folks cleaning out the "flake" that seems to be a sometime problem.
If you really get jammed up let me know as I've recently acquired a "just in case" sensor for my own store which I would (somewhat reluctantly) part with. Honestly, I couldn't bear to see you spend that kind of silly money knowing that I could have helped you out.
Cheers,
Dave
Here are the specs from the Shop Manual for testing the sensors:
Code:
testing
requires 55-pin ABS 2 - LED adapter
KDAS 0003/7
Robert Bosch GmbH
Dept: KH/VKD 3
PO Box 41 09 60
D-7500 Karlsruhe 41
Ph: 0721/4009-1
35-pin for C2 (?)
turn off ignition
disconnect ABS/PDAS control unit plug
connect 55-pin ABS 2 - LED adapter
connections (on outside of 55-pin, but available on car connector)
A - axial sensor
B - lateral sensor
C - ground for both sensors
turn ignition on
measure axial and lateral voltages; car level
shld be 2.7 +- 0.14 volts
lift car (155mm under left and right front wheels)
measure axial and lateral voltages; car level
shld change voltage; e.g.
axial
level 2.73v
left up 2.63v
rght up 2.62v
lateral (lft shld produce higher voltage)
level 2.71v
left up 2.91v
rght up 2.50v
If you really get jammed up let me know as I've recently acquired a "just in case" sensor for my own store which I would (somewhat reluctantly) part with. Honestly, I couldn't bear to see you spend that kind of silly money knowing that I could have helped you out.
Cheers,
Dave
04-21-2009, 02:07 PM
#4
Do a search, I cleaned mine using info on here. Basically unhook it, open it up, clean the metal flakes out, and put it back. I did mine a year and a half ago and it's still going strong.
04-21-2009, 02:15 PM
#5
Rennlist Member
Would thought soaking in isopropyl alcohol first to remove any metal contaminants would be worth a shot first given the cost of replacements. They are pretty simple items without much to go wrong - I suspect metal flakes/crud inside is shorting them out and the IPA will degunge them and cause it to drop out.
04-21-2009, 03:11 PM
#6
Three Wheelin'
Thread Starter
Thanks guys - all good suggestions. I think cleaning (IPA a good suggestion Ian) has got to be a first step and I might try a bench test before I come to any conclusion.
Dave, thanks for the kind offer but I think I would feel equally bad about depriving you of your "stash". Maybe a very, very last resort but if I decide to replace I'm sure there must be some available over here.
Dave
Dave, thanks for the kind offer but I think I would feel equally bad about depriving you of your "stash". Maybe a very, very last resort but if I decide to replace I'm sure there must be some available over here.
Dave
04-21-2009, 03:11 PM
#7
Three Wheelin'
Thread Starter
Thanks guys - all good suggestions. I think cleaning (IPA a good suggestion Ian) has got to be a first step and I might try a bench test before I come to any conclusion.
Dave, thanks for the kind offer but I think I would feel equally bad about depriving you of your "stash". Maybe a very, very last resort but if I decide to replace I'm sure there must be some available over here.
Dave
Dave, thanks for the kind offer but I think I would feel equally bad about depriving you of your "stash". Maybe a very, very last resort but if I decide to replace I'm sure there must be some available over here.
Dave
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04-21-2009, 03:16 PM
#8
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Dave,
I have a 'spare' accelerometer, also have the ABS and Interlock Relays - which were both faulty on my car. Luckily I was able to 'borrow' everything off another C4 and then swap everything back one at a time to prove what was good or bad. Anyone near you with a C4?
Baz
I have a 'spare' accelerometer, also have the ABS and Interlock Relays - which were both faulty on my car. Luckily I was able to 'borrow' everything off another C4 and then swap everything back one at a time to prove what was good or bad. Anyone near you with a C4?
Baz
Last edited by Sten; 04-21-2009 at 03:17 PM. Reason: Spooling!
04-21-2009, 03:22 PM
#9
Three Wheelin'
Thread Starter
Barry,
I'm pretty sure I can find a C4 locally but I think the real problem is convincing myself that a replacement works any better than mine. How on earth do you test ABS without wearing out a set of tyres?? I'm not sure I've got the cheek to pull somebody else's car to bits - particularly something as potentially expensive as the accelerometers. I'll go with the cleaning and/or testing first and see how it goes.
Dave
I'm pretty sure I can find a C4 locally but I think the real problem is convincing myself that a replacement works any better than mine. How on earth do you test ABS without wearing out a set of tyres?? I'm not sure I've got the cheek to pull somebody else's car to bits - particularly something as potentially expensive as the accelerometers. I'll go with the cleaning and/or testing first and see how it goes.
Dave
04-21-2009, 03:24 PM
#10
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Dave,
Another thing - have you checked the supply voltage to the ABS/PDAS ECU from R34 - and the condition of the pins in the plug on the ECU. They can corrode quite badly, and you only need 1 ohm resistance to drop 1 volt..
Baz
Another thing - have you checked the supply voltage to the ABS/PDAS ECU from R34 - and the condition of the pins in the plug on the ECU. They can corrode quite badly, and you only need 1 ohm resistance to drop 1 volt..
Baz
04-21-2009, 03:28 PM
#11
Three Wheelin'
Thread Starter
Up till now all the work has been done at RPM and one of their associates. I haven't had any "hands on" as yet but I intend to have a good look at all the components over the weekend and see if I can come to any different conclusion.
I find it difficult to understand how something as intrinsically straight forward as an accelerometer can fail - and then have both fail in the same way. I just don't believe it (in my best Victor Meldrew voice!!).
Dave
I find it difficult to understand how something as intrinsically straight forward as an accelerometer can fail - and then have both fail in the same way. I just don't believe it (in my best Victor Meldrew voice!!).
Dave
04-21-2009, 03:33 PM
#12
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Dave,
They may both be stuck solid (as mine were) but then you'd get the warning gong when you went over 6mph. The fault code on a Hammer is something like 'implausibale signal'. I'll come back to you, off to a TIPEC meeting pre our Factory and Museum tour next week - Stuttgart here we come!
Baz
They may both be stuck solid (as mine were) but then you'd get the warning gong when you went over 6mph. The fault code on a Hammer is something like 'implausibale signal'. I'll come back to you, off to a TIPEC meeting pre our Factory and Museum tour next week - Stuttgart here we come!
Baz
04-21-2009, 03:45 PM
#13
Rennlist Member
£1200 each winces.
I find it odd that 2 fail at exactly the same time! Also did RPM mention cleaning? I think its a pretty well known solution to 964 specialists would have thought RPM would have at least muted this as a solution.
I had an issue with the ABS on mine coming in early cleaning one of them sorted this. never had any warning lights on.
There must be a company out there that makes acceleromteters. They may not be the exact same size and have a different conector but there has to be. IIRC on a thread ages ago on here there was a guy said he could measure the outputs of a working one and find an alternative.
I find it odd that 2 fail at exactly the same time! Also did RPM mention cleaning? I think its a pretty well known solution to 964 specialists would have thought RPM would have at least muted this as a solution.
I had an issue with the ABS on mine coming in early cleaning one of them sorted this. never had any warning lights on.
There must be a company out there that makes acceleromteters. They may not be the exact same size and have a different conector but there has to be. IIRC on a thread ages ago on here there was a guy said he could measure the outputs of a working one and find an alternative.
04-21-2009, 05:44 PM
#15
Three Wheelin'
Thread Starter
I have to say that Adrian's book is a little confusing when it comes to the accelerometers. Logic says that the axial (i.e. front/back) sensor would be significant to the ABS system and the lateral (left/right) would play a part only in the PDAS operation. Adrian's book implies that the reverse is true but the Bentley book clearly shows the axial as the one immediately in front of the gear lever and the lateral in front of that further towards the front of the car. I think Adrian used the word "behind" mistakenly.
RPM did say that they cleaned them but I have no idea at this stage what "cleaned" meant. They also said that they swapped them - which doesn't really prove anything - but I agree that it seems unlikely that BOTH are faulty to the same degree.
I will probably collect the car tomorrow and will question them a little more about exactly what was done.
Regards
Dave
RPM did say that they cleaned them but I have no idea at this stage what "cleaned" meant. They also said that they swapped them - which doesn't really prove anything - but I agree that it seems unlikely that BOTH are faulty to the same degree.
I will probably collect the car tomorrow and will question them a little more about exactly what was done.
Regards
Dave