ABS problem

[littlejim]

My MOT is due this week and it will not pass with this ABS problem.

A couple of months ago I had a split N/S/F drive shaft boot, so I removed it and fitted a new one but afterwards the ABS would cut in at 5 mph.

I have taken the drive shaft out a couple of times to check it.
The ABS sensor is solid in its housing I think it would break if I tryed to move it.

I also had it checked on a computer and there was no fault codes listed.

Now the O/S/F boot is split and needs replacing for the MOT.

[jimma04]

dirt on the sensor ccause the signal to be corrupted at slow speeds this is why it cuts in a 5mph either that or you damaged the sensor or ring when you did the drive shaft

[pug-n-polo]

Its unlikely that dirt on the sensor would interupt the signals as the sensors work with magnets. Metal filings could do the trick tho! You mention that the sensor is ok but what about the condition of the abs ring?? make sure you inspect it fully and check the entire circumference for splits or cracks, or rounded/missing or damaged teeth. If that fails......

With the ignition on, use a voltmeter to check the power to the sensor. if in doubt about the result, check the other 3 sensors and match the results. The reading you get will be very low,only a couple of volts and again, should be checked against the other 3 sensors.

[jimma04]

Dirt/swarf/fileings whatever some sort of interferance, The only way to accurately check will be with an occiloscope as this is the only tool fast enough to detect something like a crack or missing/damaged tooth a multimeter will tell you that the sensor is working but not what its seeing as its sample rate is only about 3 times a second as i said it seems a bit too much of a coincidance thet you change the cv and now there is a fault. Also if its the sames as the audi a4 of similer age they are only a push fit and can be disturbed when doing this job causeing an air gap thats too big

[NickPicks]

I second (third) the dirty sensor. tHe sensors are magnetic and attract iron filings / rust particles.

The easiest way to check which one is causing the fault is if you have vag-com, use measuring blocks to log the wheel speeds from the abs sensors.

It's most likely to be the one you disturbed when you did the CV joint. I think they're a push fit, so it might have slipped out slightly, or as you hit the joint with a hammer to get it out, bits of rust fell off of the strut, dropped near the sensor and stuck to it.

[littlejim]

The ring is part of the drive shaft and I have cleaned it a couple of times, I have cleaned the end of the sensor but I haven't tried to move the sensor.

I wll have to check the voltages of all the sensors
I started to do the other drive shaft boot today. I only had time to remove the shaft I haven't changed the boot yet.

[spartacus 68]

The ring is part of the drive shaft and I have cleaned it a couple of times, I have cleaned the end of the sensor but I haven't tried to move the sensor.

I wll have to check the voltages of all the sensors
I started to do the other drive shaft boot today. I only had time to remove the shaft I haven't changed the boot yet.

When I've done the CV boots, I normally wire-brush the sensor ring on the driveshaft, then wipe-over the driveshaft housing with WD40. Complete pain to dismantle to double-check. The sensor will be in solid. If you were planning on removing, then you'll need to soak in Duck Oil Penetrating Release. Ideally needs to be tapped out from inside. If you use a screwdriver or anything else it will break.

[mdauncey]

Hi Littlejim. Did you cure this problem? I've just goth same problem on a 2005 Passat. Immediately after changing cv boot (which because of seized upper links was a bit of struggle getting joint out of bearing) I now get BS operating at the very point of stopping however gently I braake. No warning lights so presumably no dmage to sensor. Done several of these over the years on and no problems before Is only solution to strip back and clean up?