ABS Engages on Acceleration (1 Viewer)

[goldbeepbeep]

Hey all-

Recently took possession of a 2000 LX470, knowing it had this issue with ABS. Previous owner had it diagnosed at dealership being bad transfer case but the issue seemed more isolated to the ABS system, at least to me anyway.

From a full stop, ABS engages when accelerating and would bring the car to a halt. This is probably within the 3-5mph range, as ABS almost immediately kicks in when you press on the gas. When the gas pedal is tapped aggressively, the car gets closer to 10mph and it drives until full stop again. ABS never kicks in while braking (good road condition, not an issue) but only when pulling away from full stop. Because the owner thought this was a transfer case issue, I was able to negotiate down to 2,800 on a 190k mile, though torn driver seat/steering wheel and pretty badly faded paint.

I pulled out the ABS fuse in the engine bay and VSC / ATRAC / ABS lights illuminate on the dash, but otherwise drives perfectly (without ABS function obviously). Was ready to order some ABS sensors but looked through service receipts from seller and saw front ABS sensors were replaced less than 3k miles ago. I bought a live-data OBD2 reader and was unable to pull any codes/graphs on wheel speed (ABS) sensors. Did a search and found hundreds of posts with keyword ABS...must've gotten through half of them without seeing this issue ever being discussed.

Anyone here have experience or a better guess as what I need to do or should check to find the issue? With fuse back in there are no lights in the dash at all, despite having the ABS problem.

Thank you!

 

[Ayune]

Here are some thoughts/suggestions for trouble shooting:

- Try to isolate where the problem is: Unplug one ABS sensor at a time and test drive. If the issue changes then you know where to look closer.

- What do the ABS sensors ‘sense’? I would imagine they’re some sort of segmented ring, and if so, are they dirty or otherwise not triggering the ABS sensors correctly?

 

[BEG]

Make sure you have an OBD2 reader capable of displaying ABS codes. My LX had very similar symptoms when I bought it but nothing would show up on my scanner. Once I had it scanned properly, it very clearly pointed to an issue with the front drivers sensor. I replaced it with an eBay special for $13 and it's been fine ever since.

 

[goldbeepbeep]

@Ayune I'll try the unplugging in the morning and see if anything acts differently. From my last week or so of digging on the forums, I believe the sensor 'senses' a ring/bearing with teeth. I think this ring can only be accessed by removing the hub and rotors. I'm currently waiting for the 42mm axle nut socket to arrive from Amazon before I can take things apart to take a peek.

@BEG I followed a thread for someone with similar issue with their RX330 and the Launch CREADER was recommended for live-data including ABS. However, I couldn't find the function on the device and the live data section of the tool says not supported. I returned the reader to Amazon already. (LAUNCH X431 CRP423 OBD1 OBD2 Scanner ABS SRS Transmission Engine Code Reader Diagnostic Scan Tool ONE-Click Update Online PC Print)

By front drivers sensor do you mean the ABS/wheel speed sensor? I see sensors sold on eBay for about $15 vs. ones from Lexus for 10x the price. How do those hold up long term? Assuming that's the sensor you're talking about.

Thanks for the responses!

 

[saucebox]

I think you need a 54mm hub nut socket—42mm doesn't seem right at all. 2 1/8" will cross over if you can find one of those locally.

When you get there, use dielectric grease to reinstall ABS sensors so they don't get frozen in there (and you won't have to pull the rotor next time).

 

[goldbeepbeep]

@saucebox Had to go back and check - I did order a 54mm socket. Looks like my memory failed me there. Thanks for the tip!

 

[white_lx]

Would it not be the VSC (stability control) that actuates the brakes? VSC might think there is wheel slippage and activates. Is ABS not only active when braking?

There are a total of four speed sensors. It would be interesting to know why they decided to change front sensors and not the rear ones. The ABS ring on the front is protected by the rear dust seal. If never replaced it is probably deteriorated (in the rust belt).

The rear sensor ring can also get contaminated with gear oil if the rear axle seal leaks, but I'm not sure if that would affect the sensor read-out. It is easy to pull them and look inside the axle (if not rusted).

See the attached document with more info on how to test the sensors (2000 LX)

 

[Mark WV]

somewhat similar problem to what I had with a Lexus GS300 a few years back - Slowing down to a stop, the ABS would engage at low speeds for no apparent reason - The ABS would pass the self check on startup and no ABS warning light was displayed, as the sensors were fine.

However it turned out to be the teeth on the segmented ring - more commonly known as a "Tone Ring" - had been worn down by rust accumulation. One way to track it was to watch the live data from Techstream and see which wheel (or wheels) are not displaying the same speed as the others when the abs activated. When the speed signal was lost at one or more of the wheels, the system assumed the wheel had locked up, thus activating ABS.

I suspect you have one or more sensors that are either contaminated by metal shavings inside the hub, or you have a tone ring issue of some sort. When you first start the vehicle, the system will self check to see if all of the ABS sensors are responding, generally if there is a sensor problem, it will activate the ABS warning light upon startup - your issue seems to be a sensor that is not reporting the correct wheel speed for reasons mentioned above rather than a bad sensor.

I would start by pulling each of the 4 sensors (if possible) and checking for a large buildup of metal shavings. If possible also look in the hole they are mounted in to see if you can get a visual of the teeth of the tone rings to see if they are worn down. As least on the GS 300 it was the rear rings that had been damaged and it was visible in the hole the sensor came out of.

 

[Mark WV]

I just saw the post above mine regarding the VSC - same principle applies, when a wheel sensor stops reporting speed, the computer assumes a skid and activates the brakes to correct the skid.

 

[goldbeepbeep]

@Mark WV I believe the RX330 thread I read a two weeks back pretty much describes same symptoms. I've read too many threads now both related and not related...can't recall exactly. The weird thing is the car brakes just fine, either slow deceleration or hard braking. ABS does not engage (so far haven't seen rain or bad weather so this is normal behavior). However, pulling from a dead stop the problem can be replicated every single time. I'm a few days away from getting the socket so I'll be able to take a look at the tone rings. I read a closer described thread that mentions a crack in tone ring causing the ABS trigger on accelerating instead of the teeth being worn down. I'll find out soon enough I guess.

@white_lx Thanks for that! Definitely great information. Will do some searching on the rear dust seal. I read about the VSC and wheel slippage, so the first thing I did was try the center diff lock which did not help at all. But then again, if the sensor isn't reporting at all I guess it wouldn't matter how the wheels are actually spinning.

 

[Spike555]

It is your traction control kicking in for whatever reason. Traction control uses the ABS to stop the spinning wheel, this sends power from that wheel to the other wheel on the same axle.
A spinning wheel has no traction so that power is wasted, stop it from spinning and the power transfers to the other wheel which presumably has traction.

So, for whatever reason your traction control thinks the wheels are spinning. It uses the ABS sensors to make sure all the wheels are spinning at the same speed, to much difference in wheel speed and it kicks in on the over speed wheel.
Sooo....why is it doing this? Bad exciter ring on the hub? Bad wheel speed sensor?

 

[Mark WV]

I agree it could be a cracked tone ring - if you can get the sensor out, you should be able to test for that by inserting a screw driver and attempting to rotate the ring manually - if it spins independently of the axle then it is cracked.

 

[goldbeepbeep]

So while I was out this morning, the car mushed to a stop while high pitch grinding noise and engine revved. Reverses fine, but as soon as it's put into Drive the grinding begins and even persists in Park. Tried center diff lock button and was able to drive. Made it about 6 blocks home and did more reading...and got under the car to confirm the passenger side axle had slipped out about half an inch. Probably the circlip slipped off or washer/nuts came loose.

While I was under there I did inspect the ABS sensor location...and it looks like only driver side sensor was replaced despite the receipt I was shown. Passenger side has enough gunk buildup enough to look like ABS sensor is one piece with the dust shield. Along with the axle slip and what I read about power always sent to the wheel with least resistance...it does sound like what @Spike555 suggested about traction control...perhaps this was an ongoing issue with some sort of slippage and overspin at the wheel.

Going to try to get the car on some stands later and remove the hub cap to see extent of damage. The 54mm socket is yet to arrive until Saturday so might have to reassemble and wait again.

Doing lots of reading and only began trying to fix my own cars last summer. So far, the only experience I have is replacing control arms, struts, rotors and rear handbrakes on an old Avalon. Still pretty new to DIY repairs, but hope all of this can be handled...I'd rather do the work myself to learn than leave the car with a shop.

Edit: Saw videos about repacking the wheel bearings. I'm assuming this is something to be done every 30-40k miles or so to improve performance? Would it break anything if this isn't done on the car, ever? Bracing myself for any surprises I might find...

 

[white_lx]

...and got under the car to confirm the passenger side axle had slipped out about half an inch. Probably the circlip slipped off or washer/nuts came loose.

Obviously the axle should not move. The nuts only set the preload on the bearings. They do not retain the axle. If the circlip is gone, it might have resulted in excessive damage on the splines and you may not even fully drive the wheel(s) anymore or there could be a lot of play. Both cases would result in a difference between wheel and axle speed that could confuse the ABS computer. I would start there for sure. Lift the front wheel and see how much can you rotate the wheel without the axle moving. Here are some videos:

 

[goldbeepbeep]

Reporting back. Nut socket arrived and got to work. As soon as car was lifted, there was a huge amount of play in all directions and the wheel was wobbly. Removed the wheel, popped the cap and found the circlip was seated in the cap along with grease. The spline teeth as suspected was all grinded down and was perfectly smooth. The hub flange teeth does not look like it has any damage. The 2 nuts along with washers are completely unseated (guess I didn't need the socket to remove lol). I decided to temporarily tighten the nuts and with it seated, gave enough teeth for flange to catch to move the car into driveway. On starting the car, I hear a pop from under the car and a high pitch tone from the dash. Ignition off and back on. Moved the car about 20 feet into driveway and saw a trail of clear yellow oil.

Seems like an initial gush and now quick drips...anyone know what this oil is? Location is between first and second row seats on driver side under the car. Most of the drip is from that arm at the nut, there's some evidence of oil from the pan cover.

 

[Trunk Monkey]

Brake lines run along the frame right there.