My V70 Cross Country All Wheel Drive is playing up, when driving a buzzing ABS noise comes from the pedal area without even touching it, if you brake lightly the ABS activates every time and makes the pedal vibrate and click as if ABS is needed, which it is not!
Have fitted two ABS control modules (six plug type ABS/TRAC units) and cleared any fault codes to no avail, still does it!!! Help please, any ideas?
Edited by Pugugly on 28/06/2008 at 18:14
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what fault codes?
why did you replace the abs unit?
Have you checked the reluctor rings?
And on the AWD version of teh V70 - are all your tyres the same size AND brand and have similar wear? This was a big problem with them, I think volvo had some official statement that even a very small difference between the tyre diameters would cause a problem.
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The data when plugged in showed that as soon as you went over 30m.p.h. we lost the speed sensor readings to all four wheels simultaneously, it was very unlikely that all four wheel sensors could be faulty, all of the tech guys seemed to say change the ABS control unit, they always play up and we sell loads?
Tyres are all same size and have lots of tread on all of them?
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The data when plugged in showed that as soon as you went over 30m.p.h. we lost the speed sensor readings to all four wheels simultaneously
Is that actually a fault? I'm not that familiar with the volvo system, but abs will only apply at low speeds. It wouldnt surprise me that much if the signal from the sensors fades out at speed (after all its only an induced sine(ish) wave) or is thrown away by the system when it is irrelevant.
Do you actually get an error code?
What happens to the speed readings when you brake? And when the abs does its stuff?
Typically, unwanted abs activation without an error code is down to a faulty reluctor ring. I think they are built into the cv joint on the v70?
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Fair comment, what I am saying is if there is a fault with a specific speed sensor on a particular wheel wouldn't that show up on the data as we drive? it shows all wheel sensors as working, are the reluctor rings separate to the speed sensors or built in? are these the rings with teeth that pick up the signal itself?
Thanks, have had two separate Volvo tech guys at different garages on it to no avail !!!
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the reluctor rings are the toothed rings which are typically built into either the disc itself or the cv joint. basically they are fixed to some part of the drive so that they rotate at the same rate as the wheels. The sensor is fitted in the hub and detects the teeth of the reluctor ring as they pass it. On this age of car I would expect passive sensors - so you could check that they all have similar resistance (but I would expect an error code if one was bad).
you could also rig up an oscilloscope and compare the signals that you get from each sensor, that could show which corner is causing the problems.
reluctor rings can fail through corrosion filling the gaps between teeth or broken teeth or cracked/split rings(which can result in them moving on the disc or joint - giving a false impression of speed variation - especially when you hit the brakes, the disc/driveshaft/cv joint will all slow down but the now loose ring can move slightly resulting in the abs ecu detecting a wheel speed being different to the others).
that would be my guess anyway.
I would expect a sensor fault or pump/controller fault to throw an error code. a reluctor ring fault wont - it causes an incorrect reading, but so far as the abs is concerned the system is functioning correctly.
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Thanks adverse, much appreciated, that makes perfect sense and i will look carefully at the reluctor rings and wheel sensors and report back, here's hoping!!!
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Why should ABS only work at low speed-you can lock wheels at any speed!
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Is that actually a fault? I'm not that familiar with the volvo system, but abs will only apply at low speeds. It wouldnt surprise me that much if the signal from the sensors fades out at speed (after all its only an induced sine(ish) wave) or is thrown away by the system when it is irrelevant.
Why should ABS only work at low speed?-you can lock wheels at any speed.
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So, as i said in my post 28/06/08 on my 1998 Cross Country AWD, if you press the brake pedal lightly(and sometimes not at all!) the pedal judders, buzzes, clicks etc, no ABS light comes on the dash though, have changed the ABS Control unit to no avail, checked my tyres etc, has anyone had this problem on their Volvo, did you or your garage cure it? do you have any suggestions as to what to check next or what it might be? Help!! its driving me mad!
Many thanks to all
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So, the latest on this so called A.B.S. fault, the car has now visited three separate Volvo Specialist garages, (it is a 1998 S reg AWD X Country Auto) has been off the road for over three weeks, have spent a fortune on parts and labour and still as it was, no difference at all!!!!
Has had three separate ABS Modules, wheel sensors (from Volvo) every reluctor ring cleaned and checked, all wheels off, calipers cleaned, brakes bled, live data checked, No fault codes show, No lights on dashboard, But.............. start it up ,drive it down the road, and heres the bit thats got everyone, the pedal buzzes and judders as if the ABS is needed WITHOUT EVEN TOUCHING THE BRAKES, thats right, you don't even need to touch the pedal for it to happen!
I am at a loss as are the Garages that have had it, last call before it go's to Auction, I know of no other things to try. HELP!
Thanks for reading this.
{moves to previous question as related}
Edited by Dynamic Dave on 18/07/2008 at 19:17
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It happens without touching the brake pedal? Weird. Checked the brake pedal switch?
Does it have the TRACS system? I've never had that so I dont know if its all in the same unit as the ABS or if its a separate controller - but is it trying to deal with wheel spin?
Does it happen all the time or is it intermittent? Checked all the wires from the sensors back to the ecu?
The way I see it, if there is no fault code then the system thinks that it is reacting to something. I really thought the reluctor ring would be the problem.
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I am not an expert but this car is 4WD and whenever I have read any manual on a 4WD vehicle they always emphasise the need to have four identical tyres.
If there is ESP or any other kind of trickerey on the back of the ABS system an odd mixture of tyres could get it confused but not register a fault.
I would also guess that some problem with the torque sensing differentials in the transmission might also cause windup leading to the ABS getting confused.
ABS is usually simple and reliable but if the wheels are not turning at the same speed it could be very confused.
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Interesting one; I'm with AC on this - the ABS won't activate unless it's receiving a signal from either the pedal position sensor or the brake fluid pressure switch. [Have they checked these?]
Surely they can drive it down the road and watch all the switch status and wheel-speed info in live-data? Sadly; this sounds very like the almost "normal" main-dealer poke-and-hope diagnostic approach.
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I have a 1997 V70 (not 4WD) Mine started with a noise from the front wheels and pedal judder at very low speed on almost full RH lock (never LH). It then progressed to same symptoms when braking in a straight line, then became more frequent.
My local garage checked twice with no luck, then it went to Volvo for a fault test which was negative, they said it was a faulty ABS ECU which could not check its self. It was sent away for testing and today was returned as fault free!!!
At no time has it shown up any error codes.
While it has been without the ECU the problem has not occured
Edited by hemsby on 31/07/2008 at 18:16
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hemsby
That could be excess air gap on a front wheel speed sensor caused by a worn wheel bearing.
Are the reluctor rings on the driveshafts rusty or cracked?
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The car is going back to my local garage in 10 days armed with this info, will post a reply with results
Thanks
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hemsby - did you ever get this sorted. I have exactly the same build up of symptoms as your 31 July 08 post? Mine's a 25 Sept 1998 V70 XC 2.5T AUTO (AWD). It will also sometimes persist after taking your foot off the pedal. No dash ABS warning light.
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I've had many of the same symptoms in my 98 S70 T5. I had the module rebuilt and no change. As I was removing the front ABS sensors I discovered a few very small cracks in the plastic covering of the wires. Then one of the wires just came out of the plug connector. It must have become worn after the from years of repeated movement by the steering. And as of late it was intermittently causing my ABS fault (I think) until it came completely loose. The dealer has a repair kit for it. I suspect there must have developed a demand for them. I ordered two of them today. Should be in this week. Will advise.
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Facinated by this thread, I have a 1999 V70 Petrol with exactly the same problem. Just a light pressure on the brake pedal and what appears to be the ABS kicks in a causes a vibration on the pedal. It's visited 3 garages and no solution. Just tried checking the ABS control module for dry joints but again it's not fixed the problem. Intrigues to know if you ever solved the problem?
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I have a Volvo V70 XLT 1998 which has a similar problem. When the Brke pedal is touched at over 28mph there is a judder felt and a whine sound from the front of the car when it is released. this can be most disconcerting at higher speeds. The braking at speeds below 28mph is perfect and uneventful. The garage tested the OBD2 and no fault was indicated. The examined the reluctor rings and they looked fine.
How was your problem solved?
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Has anyone come up with a solution for the juddering brakes. My 1998 V70 developed the same problem. Juddering through the pedal as if ABS has come on , only more severe. Sometimes accompanied by a whine from the front left, even when ther are no kids on board. No warning lights. I have been told it might be e problem with the vacuum pump, either knackered or electical fault. Still trying to get to the bottom of it without spending too much.
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