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Problem with ABS! Any ideas?

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nick3814

New member
I wouldn't care, I was just saying the other day that mine has never gone off and I wondered if it was working ok, now it wont stop!!

Went over to the lakes today, had an excellent drive over there but once at Windemere a lot of the roads were very wet, covered in leaves and apparently a lot of the area was flooded yesterday. Anyway the car was parked up for a couple of hours whilst we went for lunch then on the way back whilst in slow traffic on a dry road the ABS came on as I pulled up to a halt, no severe braking or wet leaves, just a regular stop at a dry junction waiting for traffic to clear and then at every stop thereafter [&:] no reason at all yet braking from speed was fine only when almost stopped would it activate.....
Then I caught a bit of a pothole and as the car pumped over it the ABS light came on the dash along with the big red light with the exclamation/warning mark on it, so I pulled over, still braked ok and turned everything off for a few minutes then decided to try again, started up and pulled away, no warning lights lit but still the ABS is cutting in as I stop, same as before.....

Have any of you lads had this before? I am suspecting a loose connection on a sensor perhaps!! What do the sensors look like?

[&:][&:][&:]
 
Thanks Paul. I take it that removing the caliper and disc to check the sensor will be no different to removing a standard caliper and disc? I've never worked on a system with ABS before. Can you tell by looking at a sensor if it has failed?

Cheers
 
Not really (unless it's fallen apart). It really needs some sort of scope attaching to the sensor wires and then spinning the wheel to see if it detects the teeth on the hub. Promax fixed a long running intermittent problem on my S2 in the summer that was actually a frayed internal wire to one of the sensors.
 
Nick no problems with the ABS when I changed the discs and pads on the 996,

I'm sure someone at Tom Fergusons on Sunday morning will be able to diagnose your problem pretty quickly,

see you at the Dun Cow or give me a call if you feel its not safe to drive

Ash
 
You can spin the hub in your hand and watch the reading on a multi-meter going up and down. On my own car it turned out in the end to be the ABS computer which needed replacing. Took a long time to get to that realisation though, luckily Tref has an S2 so I verified that my ABS ECU was duff by plugging it into his car.

Have you by any chance fast charged your battery with the battery connected? I did this many times and I reckon it was either this or age that killed the ABS ECU. There is a warning in the workshop manual about using fast chargers and welding damaging the ABS ECU.

BTW if the ABS stops working you will lock the brakes up very easily. ABS cutting in at low speeds is nothing unusual, my car used to do it all the time when I used N spec Continentals.
 
The sensors can get lots of rust and scale on them but my bet would be a fragile wire or water in a plug - rain used to make my brake pad wear warning come on. Reseating all the connectors - they are clipped around the body shell in a barrel shaped thingy sorted it (front struts / inner wings, rear suspension arms)
Tony
 
Had both the front discs off today and cleaned up round the sensors, a lot of corrosion around the shields that cover the sensor and teeth, infact the drivers side will need replacing as it was shot, anyway it hasn't made any difference. I've only done the fronts as Tom Fergusuon told me he would suspect the front ones with these symtoms.
I've notice though that when it does activate as I stop I can still hear the pump faintly for a few seconds after and wondered if the fault could lie there??
 
If you hear the pump then it will be working. the dedicated ECU occasionally plays up if it isn't simple sensor corrosion or failure.
 
The thing is how do you tell without shelling out a small fortune on new sensors (£50 each + vat at euro parts) or a new ECU?
 
I would try reading the sensors first with a multimeter before buying new sensors. ECU can be tested by swapping it out with another S2 that has working ABS (which is what I did), relays can go but I can't recall the way to determine that something to do with power to the pump down in the RH wheel arch. Earth from pump to car body could also be bad. What I do recall is that from the wiring diagram the system is fairly simple in as much that there aren't many things that could be bad. Classic way of telling if the sensors are bad is that the ABS light on the dash should only come back on after driving of down the road and getting over 6 mph. From memory the ABS does some checks once the car is moving and if you have a bad wire or sensor in the sensor wiring the ABS will at this time determine a fault and turn the warning light on.
 
I'm going to check the sensors with a multimeter this weekend and wondered exactly what I should be looking for? I understand multimeters a little but I'm not sure what setting I should have it on and what sort of reading I should be looking for if the sensor is working or not.

Any ideas lads?
 
Well I managed to test the front sensors with a multimeter this afternoon (in between the showers) and both of them were giving the same reading and the same variation when the wheel was turning so I assume they are both working ok! The next step is to test the rears but then I now have a feeling it will be the ECU! Is this the unit that sits behind the wooden board in the passenger footwell? I think I might call on my mate Ashley and see if swapping his with mine solves anything, are you listening mate??

By the way I must thank Will Lyons who emailed me via the forum this morning and sent me some test data for the S2 ABS system, thanks very much Will.
 
Be very careful when you pull the carpet back, easy to pull to hard and to much and tear the carpet away from its seam around the door. You shouldn't need to pull back to much carpet as the unit is fairly close to your right ankle when driving. Once you get at the ABS unit its easy to unbolt the thing from its mount to the car, the harness though may take a fair amount of force to unclip. I recall mine being a real pain to push back in fully and equally fairly difficult to pull off, it hinges away and out from the unit. BTW mine cost about 150 quid from porschapart.
 
ORIGINAL: nick3814

I think I might call on my mate Ashley and see if swapping his with mine solves anything, are you listening mate??
Click to expand...

Listening and happy to help, Wednesday night ok with you??

 
Cheers mate [;)] tho funny enough I've used the car today and its been fine!! So we will have to see how it goes [:D]
 

ORIGINAL: nick3814

Cheers mate [;)] tho funny enough I've used the car today and its been fine!! So we will have to see how it goes [:D] 
Click to expand...

This is what happened to me, for a few months it came and went and then it finally went completely. Sometimes the light flicked on and off whilst driving along which drove me nuts.
 
Well I've finally tested all the sensors with a multi meter now, they all give the same reading and fluctuation when a wheel is turning so they can't all be buggered [&:]!! Next step is to swap the ECU with Ashes (cheers mate) and see if that makes a difference.

Its really frustrating, now as soon as you pull away the light comes on so its obviously not happy with something on the system, I can't help but think this all started when there was a lot of water on the road [:mad:] !!

I hate it when stuff doesn't work..........
 
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