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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Sat Jan 19, 2019 6:42 pm Post subject: Abs pulsing only at low speed 2mph-10mph
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Evening all!, basically have this issue with my 996 c4 1999 3.4 where as at low speed the abs pulses, bought it like this so no idea when it started nothing wrong with the brakes as such all tyres pretty good and matching and all tyre pressures correct, no warning lights or faults but this happends, has anyone successfully fixed this as upon a google search it seems a few people get this from time to time but nobody ever updates there threads as to how they’ve resolved it so it would be great to hear people’s solutions that have resolved them on here
Thanks ricky
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deMort Dijon

Joined: 21 Mar 2015 Posts: 7594 Location: Brighton
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Posted: Sat Jan 19, 2019 7:05 pm Post subject:
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It will more than likely be a wheel speed sensor thats getting old , low speed and the signal is not strong enough so the car thinks the wheel has locked up .. hence abs kicking in .
To find which one .. a fault code read out and hopefully there will be a code ..
If not then its a case of scopeing each sensor and looking for the one with the weakest signal.
You could try an ohms check on each sensor as well , youll be looking for the one thats different from the others but this is a bit of a hit an miss check.
Seperate note for any Cayenne owners .. never use an Ohm meter on these sensors .. it kills them . _________________ .
My Daughter's Crowdfunding has hit the target .
Thank you all so Very much .
She's not going until july 2020 though .
7pm - 9pm
Now At An Indy.
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Sat Jan 19, 2019 7:10 pm Post subject: .
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Great advice thank you!, I was thinking along that same path either speed sensor or the ring bit inside that the speed sensor uses, doesn’t seem to be any fault codes so I’ll try and test them see what there all reading and will update you guys either way, have you had this problem before on yours?, I guess there’s not much else it could be since there’s no warning lights etc and no other braking issues other than this at low speeds
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deMort Dijon

Joined: 21 Mar 2015 Posts: 7594 Location: Brighton
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Posted: Sat Jan 19, 2019 7:18 pm Post subject:
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I think the ring whilst posible might tend to give you problems at higher speeds .. have a look at each one though , your looking to see if they are heavily corroded ... and i mean VERY heavily corroded .
Off hand i would start with looking at the sensors .. some testers give you a value as the car moves so you would see x3 wheels at 5 mph and x1 at 0 if it is a sensor or a ring .
Ive not had it before on mine .. i dont actually own a Porsche im afraid .. im a Porsche Mechanic  _________________ .
My Daughter's Crowdfunding has hit the target .
Thank you all so Very much .
She's not going until july 2020 though .
7pm - 9pm
Now At An Indy.
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Sat Jan 19, 2019 7:34 pm Post subject:
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Agh I see I’m not sure if my friends diagnostics shows up individual wheel speeds x4 but I’ll look into it as that would be a much easier way to pin point the problematic corner for sure
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deMort Dijon

Joined: 21 Mar 2015 Posts: 7594 Location: Brighton
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Posted: Sat Jan 19, 2019 8:54 pm Post subject:
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Just for us nerds here ..
The sensor is a magnet with copper windings.
When you pass a soft iron metal over this it will generate a small voltage .. emf i belive (Electro Motive Force ).
The sensor will have a metal part then a gap then a metal part going in front of it .. this will in turn generate a voltage then no voltage then a voltage in the sensor .. an oscilateing signal basically .
The car sees this as a waveform and knows the rotation speed of the wheel due to the frequency of said wave form.
If something interupts this signal be it a poor / corroded ring the pattern will alter to a flat point at times , low speed and this is far more likely due to corroded highs and lows of the rings , corrosion will almost join two high points of the ring together .. or a poor sensor that cant generate a descent signal .
If you have a fast enough scope then you will see a square wave .. the reality is most scopes show an analog signal or a slope up / down . _________________ .
My Daughter's Crowdfunding has hit the target .
Thank you all so Very much .
She's not going until july 2020 though .
7pm - 9pm
Now At An Indy.
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Sat Jan 19, 2019 9:57 pm Post subject: .
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Thanks for that it’s quite an interesting little read I’m looking forward to getting started on it now and getting to the bottom of it now!, I’ll have it plugged in tomorrow see exactly what info we can extract from the diagnostics before I start stripping and inspecting the rings etc. Thanks for your help!
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HSC911 Long Beach

Joined: 23 Jul 2014 Posts: 6762 Location: Bedford
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Posted: Sat Jan 19, 2019 11:18 pm Post subject:
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Don't forget to donate too
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Griffter Spa-Francorchamps
Joined: 22 May 2016 Posts: 368
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Posted: Sun Jan 20, 2019 7:47 am Post subject:
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I had exactly this on my wife’s rover years ago. It was a cracked reluctor (ABS) ring. My moneys on a senor or ring.
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Sun Jan 20, 2019 3:03 pm Post subject:
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Yea I agree one or the other, don’t think will get chance to have it plugged in wile next weekend now but will certainly update you guys in the hope that it helps somone else too, can the abs ring bit be changed if it is that or is that part of the drive shaft of these?
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wasz Sepang
Joined: 28 Dec 2012 Posts: 2998
1999 Porsche 996 Carrera 2
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deMort Dijon

Joined: 21 Mar 2015 Posts: 7594 Location: Brighton
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Posted: Sun Jan 20, 2019 8:47 pm Post subject:
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Im afraid the ring is part of the driveshaft .. you are looking for x2 ring high spots almost joined together .. you can scrape out the rust between the two .. that is if thats the fault .
Figure out which corner of the car is the problem first then go from there . _________________ .
My Daughter's Crowdfunding has hit the target .
Thank you all so Very much .
She's not going until july 2020 though .
7pm - 9pm
Now At An Indy.
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Mon Jan 21, 2019 8:48 pm Post subject:
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Little bit of an update plugged it in today no faults stored, tried to get the values of all 4 speed sensors on durametric diagnostics and annoyingly I can’t seem to get it to show anything it doesn’t do anything, will check it out on my friends diagnostics at weekend
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Sun Jan 27, 2019 4:11 pm Post subject:
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Bit of an update done a diagnostics and no faults, done a scan of the abs sensors and nothing flagging up as out of ordinary so guess it must be the abs ring either damaged or rusty/corroded
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JS1500 Monza

Joined: 12 Apr 2017 Posts: 211 Location: Aberdeen
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Posted: Sun Jan 27, 2019 9:39 pm Post subject:
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I had this fault on my C4 and found a garage that could replace the reluctor rings without having to replace the driveshaft.
I actually have a couple of spare rings, as I bought four. If they're the same as the ones you need you can have them for the cost of postage... _________________ 2000 996 C4 - Guards Red
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Sun Jan 27, 2019 9:56 pm Post subject:
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Great thanks that’s the best thing that I’ve heard as it does seem very plausible that being the fault but then I’ve not heard of anyone else having issues with the rings so worried I’m heading in the wrong direction, was your symptoms the same as in abs pulsing but only at very low speed?
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wasz Sepang
Joined: 28 Dec 2012 Posts: 2998
1999 Porsche 996 Carrera 2
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Posted: Mon Jan 28, 2019 11:04 am Post subject:
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Rickyhull wrote: | Bit of an update done a diagnostics and no faults, done a scan of the abs sensors and nothing flagging up as out of ordinary so guess it must be the abs ring either damaged or rusty/corroded |
Can this diagnostic log all 4 wheel speeds?
Then drive the car in a straight line and see which one is out compared to the others.
Then you can start to look for them.
When I fitted new front wheel bearings to my C2 Im sure the wheel bearing seal had something written on it to say it has the reluctor in. But yours being a C4 will be as DeMort says on the driveshafts. _________________ My special order MY99 Vesuvious Charcoal 996 | Clutch, Fly RMS IMS AOS Job |
Steering Rack Hard Lines | Air Con Compressor / System
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Mon Jan 28, 2019 12:30 pm Post subject:
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Unfortunately not on my friends although I have got durametric and it does show up all 4 wheel speed sensors but doesn’t give off speeds/voltages so maybe because it’s the free version I’m not sure 👎
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Rickyhull Monza
Joined: 06 Mar 2016 Posts: 211
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Posted: Fri Feb 22, 2019 2:10 pm Post subject: Update
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Bit of an update checked abs rings and all seem ok, not sure what the next best thing to do is, does anyone hav a link to a free download fault code reader so I can read live data to see which wheel seems to be reading differently to the rest? I’ve got a durametric cable and program free one off the internet but can’t seem to get it to do anything on the live data for wheel speeds
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easttorks964cab Monza

Joined: 02 Jun 2008 Posts: 151 Location: East Yorks
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Posted: Sat Feb 23, 2019 6:29 am Post subject:
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Ricky (OP), if it helps, I agree with demort on the wheel speed sensor. As daft as it may sound on a 911 site, one of my work vans had the same problem and it was the sensor....same symptoms and the same diagnosis as demort suggests. if its not the sensor, then its probs the bearing (as the two work in tandem). I hope this helps.
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