Repeated ABS Front Sensor Fault

[Green RT]

By 99RT often gives me a hard ABS fault. Alternating lights that require grounding Pin 2 to reset. Sometimes I can go days without a fault. Sometimes it faults within a few feet of driving off. Sometimes it faults when the front wheel goes over a bump at slow speed. If I get past the first 50 feet/meters, it usually stays out of fault mode for the duration of the ride. The Fault Code is 3 = Front Sensor. I have checked the gap. The cable looks okay, but who knows. I have a jumper attached to Pin 2 that I have brought out from under the seat. I have probably reset it 100s of times in the past couple of months. I have even thought about putting a push button switch on the dash to ground Pin 2. But really I ought to fix it.

 

Any suggestions to try before I pull the trigger and order a new front sensor.

 

Thanks,

[John Dickens]

I posted the identical problem last week. I've even metered up the sensor resistance and it seemed OK. I was just about to change the whole unit but replies to my post suggested that I change the sensor. Apparently it can still be useless even if it seems to be A1.

[bcarlson]

Check the cable. Again. I suspect there is a wire tie that is causing a very tight bend when you turn the bars. The wire is intermittant there, or at least it was on mine, 60k ago.

 

Bob

[big-t]

Sometimes it faults when the front wheel goes over a bump at slow speed. If I get past the first 50 feet/meters,

 

Check the front wheel for side to side movement,its sounds like the sensor gap is varying when it hits a bump,also check the gap as you rotate the wheel around.

 

If everything is tight,rotate the wheel until the sensor gap is at its widest spot and recheck the gap setting,set it to the specification and then rotate the wheel and make sure the sensor clears the exciter ring all the way around.

 

You could also compare the resistance in the front sensor against the rear one.They should have the same values...or pretty close.

[flars]

I wonder if the bobbins in your front wheel are worn. I would think that if there is excess movement of the disk you would get faults on start up (sometimes) and on bumps (sometimes).

I am at the point where I have some radial movement in the disk, and so I will be replacing the bobbins soon.

[John Dickens]

I wonder if the bobbins in your front wheel are worn. I would think that if there is excess movement of the disk you would get faults on start up (sometimes) and on bumps (sometimes).

I am at the point where I have some radial movement in the disk, and so I will be replacing the bobbins soon.

 

The toothed abs ring is inside the bobbins and is bolted solidly to the wheel hub. Play in the bobbins couldn't cause the abs ring to float.

[Green RT]

Check the front wheel for side to side movement,its sounds like the sensor gap is varying when it hits a bump,also check the gap as you rotate the wheel around.

 

If everything is tight,rotate the wheel until the sensor gap is at its widest spot and recheck the gap setting,set it to the specification and then rotate the wheel and make sure the sensor clears the exciter ring all the way around.

 

You could also compare the resistance in the front sensor against the rear one.They should have the same values...or pretty close.

All good suggestions. I haven't looked at whether there is any play in the front wheel or any variation in the clearance. I doubt it, but it is easy to check (It is below freezing in the garage right now, so I will wait a bit before checking it).

[BMT]

... I've even metered up the sensor resistance and it seemed OK.

(Sorry, I thought I had posted to that thread, but apparently not ... must be an age thing!)

 

It's not unusual for electronic circuits to test okay under static conditions, but fail under dynamic (normal working) conditions. It's certainly possible that the sensor takes too long to switch between 'on' and 'off' states (long rise/fall time), for example, so that when the wheel is at speed, the pulses disappear.

 

Changing the sensor is a relatively cheap diagnostic step. It isn't always possible to make an absolute diagnosis without some expenditure. Better than changing the central ABS unit and still having the fault ...

[Joe Frickin' Friday]

Changing the sensor is a relatively cheap diagnostic step.

 

Well, cheaper than a new ABS brain, but more than a cheeseburger: the sensor was upwards of $100 when I replaced mine a few years ago. Affordable, but not something you buy on a whim.