ABS Woes!!

[Error404]

Gapping the sensors is pretty basic - push them in all the way, until they touch the ring. Then pull them out 0.5-1.0mm.
Maybe its not the gap, in which case you need to get a scope on the sensors, measuring AC voltage.
You can then compare the readings from the 4 sensors, either by running the car on the ramp or on the road (road would be a better test).

[A80Avant]

Hmm
Gets a bit more complicated. All sensors are new which makes it be a bit weird situation.
I'll pass on the details and see if I can get a voltage measurement

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[Error404]

You need to compare the sensors output to see which one(s) is triggering the fault

[A80Avant]

Went for a drive and when the ABS comes on there is a small hissing sound coming from the ABS pump area. In addition the brake warning light comes on as well.
Other than the sensor and brake fluid level being the culprit, what other reasons to get the warning light to come on?
System on a vacuum servo of course.

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[steve briance]

have the new sensors all got continuity?

oscilloscopes are not something most people have but multimeters more likely. Check for continuity, it is not beyond the realms of possibility a new sensor if faulty.

The last fault i had with my ABS was pretty much the same as yours even down to being intermittent before completely giving up and running the pump all the time with light on dash.

checking the ABS wiring plugs one by one under the bonnet and under the back seat (the nearer the ABS ECU the better as that will find wiring faults along more length of wire) showed me the offside rear circuit was faulty (no continuity) and then tracing the wire back, i found it had been chafing against the rear wheel and rubbed through.

Open circuit, no ABS.

[mcandmar]

I just replaced one of mine yesterday as it started cutting in intermittently like that at slow speeds, then eventually just gave up so the ABS light was on permanently. The faulty sensor was only 3-4 months old, one of those £14 ebay jobbies. The other three are all factory original, go figure.

When i initially fitted it i had to readjust it a few times to get it working properly, seems they are very fussy about distance. As above i just pushed it in until it bottomed out, then pulled it back a hair. i.e. a fraction of a mm. I was tempted to leave it bottomed out to grind its own clearance

Question is, did you buy those cheapo A4 sensors, are factory original?

[Mikes2]

A good sensor normally measures around 1200-1400 ohms resistance

[A80Avant]

Thanks for that Mike

I managed to find what seem to be new sensors with original plugs. But I don't know what the oem make are so I don't know.

[Mikes2]

Originals are normally Wabco

[A80Avant]

ABS update.

We found that 2 sensors are at 1240ohm one at 1100 and one was at 1700ohm

We replaced the last one with one that was at 1150ohm.

Problem still persists.
All distances were checked and no faults are found. ABS operates just before you reach a standstill at less than 20km/h, more like 10km/h

In at a loss... other than trying to find oem sensors which I'm not sure they are available anymore I can't think of what else to do.

[mcandmar]

Have you ruled out the possibility of a damaged ABS sensor ring, all you need is one dodgy tooth for it trip the sensor at low speed. Also double check that are your wheel bearings all good and without and play, a worn bearing can have a surprisingly amount of movement.

[A80Avant]

Bearings are new. I'll ask about the rings

[Tom_]

Any udpates?Problems solved?Because it looks like i have a similar problém :/

[A80Avant]

Yes. It was as mcandmar suggested. One of the rings had been knocked and we think that once that was replaced it cured it.

[Tom_]

Hows damaged?Cause u wrote, that everything was new, isnt it? Missed one tooth on ABS ring? And gap of the sensor and ring, was to the max (close) ?