ABS intermittently activated

[Pieter Naude]

I have joined the LC Club as a last resort in finding answers to my problem. I have a 2000 model Land Cruiser Cygnus V8 with 265 000km on the clock, in perfect condition. Never broken down, never not started. Ever since I had it the ABS system gets activated automatically and intermittently without warning (3 - 6 - 12 months in between activation) All incidents happened on good tar roads at speeds of 80-100km/hr. I have tried all of the following, but without success. New tyres, checked wheel balancing and alignment, cleaned sensors on each wheel, electronic diagnostics (no recorded incident) and gave Cruiser to local Toyota to test and fault was replicated. They contacted Lexus (Sygnus) specialists in South Africa and Japan without an answer. My wife doesn’t want to ride with me anymore and wants me to sell the best vehicle I ever had. It is a lounge on wheels and takes me everywhere. As a final attempt I considered having ABS deactivated, but concerned about safety. Hope someone has a Solution!
Thanks

 

[uHu]

Welcome to the forum.
What do you mean by "ABS activated"? ABS is supposed to prevent your wheels being blocked when braking, but I presume you are saying that something else is happening.

 

[Pieter Naude]

The wheels lock/brake and release continuously just like when ABS comes on during a hard brake. It is a shudder for a few second and then stops when I slow down.

 

[StarCruiser]

Hi Pieter and welcome. This could be due to a buildup of rust on reluctor rings on each axle or on the ABS sensors, but you say these have been cleaned. It could also be a break in a reluctor ring. Sometimes rust gets underneath them and forces a break. This is generic info, I don’t know your model of truck but if the reluctor rings are external (the 80 series run inside the steering spheres) this could be happening.

 

[Pieter Naude]

Thanks for the replies so far. Much appreciated. The attached show my Cruiser (CYGNUS). Another interesting but weird observation was that the ABS was activated on 4 occasions, many months apart at the same spot on the road. The only commonality was a big cell-phone tower next to the spot. Weird because it begs the question - can outside electronics interfere with the Cruiser electronics/sensor/actuator?

 

[Chris]

The tips of the ABS sensors are magnetic and as the magnetism starts to fail, the ABS will fault occasionally. This doesn't show up as a fault, electrically. What also happens is that you get wear in the CV joints, wheel bearings and bushings in the hubs. This means that the distance between the ABS ring and the tip of the sensor can change and be out of spec. It's all marginal stuff that at times adds up to an ABS failure. Does the ABS fault light come on on the dashboard?

 

[Pieter Naude]

Thanks Chris, this seems to make sense and I will report your reply to local Toyota workshop. In answer to your question - the ABS light does come on and as soon as shudder stops, light goes off.

 

[StarCruiser]

Interesting stuff about the cell phone tower. The answer to your question is ‘possibly’. Combined with Chris’s comments, a weakened relationship between the magnetic pickup and the reluctor (ABS) ring could possibly mean the pickup could be affected by an outside strong radio source. A bit like picking up a foreign radio station bleeding over when there are certain atmospheric conditions. There have been many cases of such things, though this is the first time I’ve heard of this one. If you can make it repeat with any certainty at the same spot, I’d say you have a case of EMI (ElectroMagnetic Interference). There may be a simple way to cure it if this is the problem, but you’d need to be able to replicate it reliably first. If you do, I am in contact with one of the foremost authorities on the subject. I am thinking that adding ferrite cores to the sensor cables may help reject this interference as it is one tool in the box. This is a guess though and may do nothing but ferrite cores are very cheap and easy to apply, at least at the sensor end as they clip over the cable. You may well need them at the ABS controller end as well. This may be less easy to fit due to location, wire bunching in looms etc.

See if you can replicate it first, and keep us posted.

Of course, sensors do go bad. I’ve just had the crank position sensor on the Cursed Smart Car fail, stopping the engine twice with weeks in between then more frequently before it wouldn’t go at all. That is the same type of sensor.

 

[Richard Turner]

Does it have dynamic stability control or similar? I had the same problem with a BMW, you drove along a straight road and suddenly the stability control would try and straighten the car out with the abs brakes, it turned out to be a faulty Yaw sensor that was located under the passenger seat, it was telling the car that there was a high lateral G force and that the car was skidding, even though you were just driving normally.

 

[flint]

This looks like quite a handy thing for checking the ABS rings, http://www.ate-info.de/en/details/produkte/testkarte-fuer-magnetische-sensorraeder (about £25ish on Amazon) though probably better for unitary hub assemblies. But +1 on sensors losing strength or going intermittent, I had a Hall sensor that caused difficult to pin down problems until it finally failed totally. Interesting small mention of EMI effect on plane and car ABS here:https://www.emcia.org/awareness/Pages/InterferenceExamples/Automotive.htm

 

[StarCruiser]

Interesting Flint, good find on the EMI article. By the looks of it, fitting ferrite cores to the cabling may have no effect but it would be a very cheap thing to try.

That little card tool for the ABS seems to be for a later design of impregnated rubber speed sensor ring rather than the toothed reluctor rings. I’ve not seen these so don’t know if the OP’s truck has them or the toothed rings.

 

[flint]

I think you're right on the ATE thing, you could probably do a similar thing with a stiff plastic folder and some iron filings perhaps. I nearly bought one when my wifes car was having ABS problems. It turned out, when I checked, that the local main dealer had messed up fitting a new front hub assembly (used a press instead of the proper special tool) and the hub hadn't locked on properly allowing the rubber ring to move out of alignment with the sensor (and possibly eventually the whole lot falling off). Stiff words were had !

 

[Pieter Naude]

Thanks to everyone for taking the time to reply. I have forwarded all the responses to a Toyota South Africa, through their local agent. Have a great weekend

 

[JuanKzn185]

Hi did you ever find the problem? I also have a uzj100 that does the same thing.

 

[Quentindp]

Any further progress or solutions on the matter, Pieter? Same problem here on prado 120