ABS - Antilock warning light on UPDATE
07-07-2003, 06:41 PM
#1
Burning Brakes
Thread Starter
ABS - Antilock warning light on UPDATE
Couple of days ago I started my 951 and begun to drive. I noticed immediately, that it didn't make that "phuuz"kinda noise from the ABS - system. And after a couple of second driving the light came on. And I tried the brakes, ABS didn't work. 
So what to expect? €€€€ $$$$ how much?
Is there some common failure?
So what to expect? €€€€ $$$$ how much?
Is there some common failure?
07-07-2003, 07:17 PM
#2
Nordschleife Master
I suppose it could be the brain but since the light goes out then comes back on I think the common failure is the wheel speed sensors.
Once you get rolling the brain checks the respective wheel speeds and if they are not within, I have been told, ~ 7% of each other you fail the test and it shuts off. People have done this with mismatched tires or for some reason a wheel speed reference sensor has failed or the sending wire cut.
Once you get rolling the brain checks the respective wheel speeds and if they are not within, I have been told, ~ 7% of each other you fail the test and it shuts off. People have done this with mismatched tires or for some reason a wheel speed reference sensor has failed or the sending wire cut.
07-07-2003, 07:25 PM
#3
Burning Brakes
Thread Starter
Yeah, that was my though too, that it is not (hopefully) the brains, because it does go away, after the engine has started. And it comes back on again after few feets drive.
Are those speed sensors expensive / difficult to change?
And is there any way to tell, which wheels sensor is broken?
Are those speed sensors expensive / difficult to change?
And is there any way to tell, which wheels sensor is broken?
07-08-2003, 03:23 AM
#5
Burning Brakes
Thread Starter
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Sami951:
<strong>bump</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">make it a douple..
I guess I'm the only one with brake troubles?
<strong>bump</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">make it a douple..
I guess I'm the only one with brake troubles?
07-08-2003, 03:41 AM
#6
Nordschleife Master
I don't know the best way to go through this guys since it never happened to me. I was just BSing with a former Porsche team race driver from Austria on an airplane flight and asked him what the whirring sound was when the car finally got rolling.
And he also mentioned some of the problems of the ABS.
If you are going to do this yourself get ready for a lot of wheel changes. First clean things up and examine the wires and sensor. You may be Ok then.
Next get one new reference sensor and trade it around all the wheels and see if one of them was the problem. Usually is just one. I believe if you have the error code tool it may pinpoint the problem, but I don't recall the conversation well enough for that point as it was quite a few years ago and we were drinking pretty good and covering a wide range of topics. <img border="0" title="" alt="[Wink]" src="wink.gif" />
And he also mentioned some of the problems of the ABS.
If you are going to do this yourself get ready for a lot of wheel changes. First clean things up and examine the wires and sensor. You may be Ok then.
Next get one new reference sensor and trade it around all the wheels and see if one of them was the problem. Usually is just one. I believe if you have the error code tool it may pinpoint the problem, but I don't recall the conversation well enough for that point as it was quite a few years ago and we were drinking pretty good and covering a wide range of topics. <img border="0" title="" alt="[Wink]" src="wink.gif" />
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07-08-2003, 04:12 AM
#9
Nordschleife Master
TT, I'd pull the wheels off and clean things up real good. That really might do it.
A local tuner is not real happy with stand alone Electromotive engine management for the 911 series because crud builds up and messes up the HAL reference sensor. You have the same technology that is exposed to the elements on your ABS so it is sure worth a try.
A local tuner is not real happy with stand alone Electromotive engine management for the 911 series because crud builds up and messes up the HAL reference sensor. You have the same technology that is exposed to the elements on your ABS so it is sure worth a try.
07-08-2003, 04:22 AM
#10
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Also, there is an ABS relay under the hood. If you pull it out the light goes on. Check relay first. It is a silver looking (an aluminum casing) relay in the fuze box. There is an insulation plastic tab inside it. When relay is shaken it rattles which made me (mistakenly) think it is bad. I opened it, but the relay was ok... Check it at your local auto parts store based on a diagram on the case.
Wheel speed sensors aren't to hard to replace - one alen bolt and a connector. Dirt "likes" to build up in there, cleaning it would be your first step!
Hope this helps!
Wheel speed sensors aren't to hard to replace - one alen bolt and a connector. Dirt "likes" to build up in there, cleaning it would be your first step!
Hope this helps!
07-08-2003, 04:38 AM
#11
Rennlist Member
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Sasha:
<strong> Dirt "likes" to build up in there, cleaning it would be your first step!</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I agree. It sounds like you just have dirty sensor plugs. I had the exact same problem after replacing my brake pads. Took each wheel off one at a time to clean the sensor plugs (they're inside locking plastic covers), made sure they were deeply seated in the sockets, and the problem went away.
Cleaning or adjusting the sensors themselves would be your next step. I believe Pikey recently went through this. It's pretty well described in the Factory Shop Manuals.
Good luck. It should be no problem.
<strong> Dirt "likes" to build up in there, cleaning it would be your first step!</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I agree. It sounds like you just have dirty sensor plugs. I had the exact same problem after replacing my brake pads. Took each wheel off one at a time to clean the sensor plugs (they're inside locking plastic covers), made sure they were deeply seated in the sockets, and the problem went away.
Cleaning or adjusting the sensors themselves would be your next step. I believe Pikey recently went through this. It's pretty well described in the Factory Shop Manuals.
Good luck. It should be no problem.
07-08-2003, 04:41 AM
#12
Burning Brakes
Thread Starter
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" /> guys..
I promised to my gf, that we're gonna go and see the "ricey" movie 2fast2furius part 2 today, but I'll be spending our quality time evening in the garage.. <img border="0" title="" alt="[Wink]" src="wink.gif" />
I promised to my gf, that we're gonna go and see the "ricey" movie 2fast2furius part 2 today, but I'll be spending our quality time evening in the garage.. <img border="0" title="" alt="[Wink]" src="wink.gif" />
07-08-2003, 05:38 AM
#13
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Hi Tommy,
Don't worry, You're not alone!
I have exactly the same problem. I've cleaned the sensors, replaced the sensors, cleaned the hubs, tried a new relay. All to no avail.
Two possibles.
Have you checked the OD of your tyres? apparently, if it's off, then the ABS can't function.
Have you checked the relays on the ABS unit itself? That's my next port of call..... Gonna get the parts when i'm in the UK next week and spend a couple of hours crawling under the passenger side wheel arch!
Let us know if you fix it!
Don't worry, You're not alone!
I have exactly the same problem. I've cleaned the sensors, replaced the sensors, cleaned the hubs, tried a new relay. All to no avail.
Two possibles.
Have you checked the OD of your tyres? apparently, if it's off, then the ABS can't function.
Have you checked the relays on the ABS unit itself? That's my next port of call..... Gonna get the parts when i'm in the UK next week and spend a couple of hours crawling under the passenger side wheel arch!
Let us know if you fix it!
07-08-2003, 10:06 AM
#14
Burning Brakes
Thread Starter
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by pikey7:
<strong>
Two possibles.
Have you checked the OD of your tyres? apparently, if it's off, then the ABS can't function.
Have you checked the relays on the ABS unit itself? That's my next port of call..... Gonna get the parts when i'm in the UK next week and spend a couple of hours crawling under the passenger side wheel arch!
Let us know if you fix it!</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">the tires should be ok, 'cause I haven't changed them.
Don't know about the ABS unit's relay.
I did check the relay in the fuse box, is there some other as well?
<strong>
Two possibles.
Have you checked the OD of your tyres? apparently, if it's off, then the ABS can't function.
Have you checked the relays on the ABS unit itself? That's my next port of call..... Gonna get the parts when i'm in the UK next week and spend a couple of hours crawling under the passenger side wheel arch!
Let us know if you fix it!</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">the tires should be ok, 'cause I haven't changed them.
Don't know about the ABS unit's relay.
I did check the relay in the fuse box, is there some other as well?
07-08-2003, 10:06 AM
#15
Addict
Rennlist Member
Rennlist Member
Your ABS system is failing BITE check, on drive-off. That's the "phuuz" kind of noise you're hearing - it runs the pump motor and cycles the valves after drive-off to make sure everything's working. Clearly it's not. This indicates that either the pump motor relay or valve relay are not working and need to be replaced, most likely. The failure of the pump motor, while not impossible, is quite unlikely.
The brain or ECU runs a self-diagnostic on key-up (ignition on). If the lights go out after starting the car, the brain is fine, as it will not clear the lights until it successfully passes the test.
However, if the light does not go off after key-up, that doesn't mean the brain is fried. The wheel speed sensors are tested initially on key-up, then again monitored on driving. The initial key-up test is for continuity in the sensors, and so will catch an unplugged sensor or broken wire. After driving starts, the wheel speed signals are continuously monitored for plausibility, compared against eachother. If the light comes on after the initial drive-off BITE check (when the motor and valves are actuated), then it's most likely a plausibility fault on a wheel speed sensor. This is the failure that can be caused by mis-matched tire diameters, if the mis-match is big enough. IIRC it's over 6% difference in the rolling radius, but YMMV, that's older software than I'm used to dealing with.
Will somebody please archive this stuff??? This should be a complete or fairly complete run-down on the basic failure modes of the ABS system. The next step would be to pull codes. Sometimes these can be obtained by a flash code, but I don't know about these cars. Depends on the manufacturer. Will have to check it out someday.
The brain or ECU runs a self-diagnostic on key-up (ignition on). If the lights go out after starting the car, the brain is fine, as it will not clear the lights until it successfully passes the test.
However, if the light does not go off after key-up, that doesn't mean the brain is fried. The wheel speed sensors are tested initially on key-up, then again monitored on driving. The initial key-up test is for continuity in the sensors, and so will catch an unplugged sensor or broken wire. After driving starts, the wheel speed signals are continuously monitored for plausibility, compared against eachother. If the light comes on after the initial drive-off BITE check (when the motor and valves are actuated), then it's most likely a plausibility fault on a wheel speed sensor. This is the failure that can be caused by mis-matched tire diameters, if the mis-match is big enough. IIRC it's over 6% difference in the rolling radius, but YMMV, that's older software than I'm used to dealing with.
Will somebody please archive this stuff??? This should be a complete or fairly complete run-down on the basic failure modes of the ABS system. The next step would be to pull codes. Sometimes these can be obtained by a flash code, but I don't know about these cars. Depends on the manufacturer. Will have to check it out someday.