Topic

My ABS light keeps coming on and going off again......

I thought it was the tracking but after having that done this weekend it has just come back on again .

I have had some work done underneath so I think it could be a sensor/wire problem as when we plug in the diagnostic thingy it only tells me to change one of my spark plugs and doesn't mention the ABS???

Help please is there anyway I can find out why it is doing this - it tends to come on when go round corners and it doesn't matter which direction.

Ruth

The fact that the problem is intermittent is possibly going to make it difficult to track down, as Sod's law dictates that:
"Everything will work perfectly whist being tested, checked or watched, and the fault will only return when it isn't possible to find the problem."

Having shared those comforting thoughts with you.
As you say the problem comes and goes with steering the wheels, the first place I'd look is the front wheel sensors, their wiring and earthing.
From there I'd check the rears, then check the 10 amp fuse (#20 under dash), 60 amp fusible link (#2 under the bonnet) and wiring connections to the ABS, making sure they are secure and aren't corroded. Now the fact that the problem comes and goes means the fuse and fusible link won't be blown, but it is possible their terminals are corroded.
Also check the ground wire for the ECU and its connection.

I've just noticed your car is a TF not an F so those fuse numbers and locations will be different, I've not worked on a TF so I can't tell you which fuses they are, but I'm sure someone will be along to tell you, but the rest of the above should still apply.

When you first switch on the ignition the ABS unit will do a self test, if all the circuits have continuity and there is a resistance from the pulse transducers (wheel sensors) the light will go out after a few seconds, all is OK.

If the light comes on while you are driving then one of the wheel sensors is probably missing some pulse information from the reluctor rings.

These rings are mounted on the inside of each hub and look like gear teeth as the wheel revolves the wheel sensors pick up an inductive signal from the teeth, the ABS unit looks at the information from all 4 wheel sensors and if any sensor stops giving a signal it assumes the wheel has stopped turning, if you are applying the brakes at the time then ABS unit will pulse the brake circuit pressure to that wheel to allow steering and stop the wheel from locking up, if you are not braking a fault is assumed and the ABS warning light will come on.

If there is rust build up on the rings or dirt on the base of the sensors It will start to skip pulses, there is an allowable amount of differentiation between pulses from each wheel to allow for turning as the wheels on the outer of the turn will rotate faster than the wheels on the inner of the turn due to the different radii, also a mix of new and worn tyres will have a different rolling radius.

As your light is only coming on when making a turn it looks like rust build up on the rings or dirt on the base of the sensors which is going beyond the allowance.

I would wire brush the reluctor rings and clean the base of the sensors. The sensors also have a ferro magnetic core so any magnetic particles like rust etc. will stick to them and also give the false information to bring the ABS light on.

Brian.

I had a similar fault, not on the F, but on my Alfa 159, and it turned out to be that the wire from one wheel sensor had chafed through its insulation where it passed through the wheel arch, and was occasionally shorting to earth.
The damage was hidden until the plastic wheel arch liner was removed, and it was, (of course), the 4th wheel arch liner that I removed which revealed the problem, (I'd started at the front as it was induced by cornering, thinking that turning the wheels must be doing it, but it was the offside rear.). I cut out the chafed section and soldered the ends back together before wrapping in self amalgamating tape. and it's been OK for several years now.