Lexus rx300 abs problem

Thanks in advance to all that try to help me out, I really need help on this one before the snow falls.

2000 Lexus RX300 with ABS and Traction control, 170,000 miles, overall great shape.

Brain teaser for you Lexus brake guru’s
The following started happening this summer and continues today, I was hoping it would get worse so I could find it easier, but no such luck.
ABS kicks in when just about stopped, BUT I don’t feel a pulsation in the steering wheel but do in the brake pedal.
No ABS light on except for 3 or so seconds when starting the car- normal.
No codes using ABS dash light method and shorting pins x and y.
No codes using ABS dash light method, shorting pins x and y, then driving straight for 30 seconds and then reading codes via dash ABS light
Pull the ABS fuse and no longer acts up, but no ABS and dash light is then on.
Front wheel sensors ok, ~1.6K ohms and no shorts to ground.
Rear wheel sensors ok, ~1.2k ohms and no shorts to ground.
Used Mic input to laptop and oscilloscope software to monitor wheel sensor signal output one wheel at a time, all four wheels had same pattern, amplitude, and from what I could tell approximate frequency. Since I could only monitor one wheel at a time I could not do a real time compare of the output from one wheel to the others. Note, back probed at the ABS ECU so this should rule out bad wiring to the ABS ECU.
Note: Alldata wiring diagram for this car (2002 RX300 with ABS and Traction control) does not align with what’s in the car. The 2002 RX300 with only ABS and no traction control does match up, very strange.

Replaced the ABS ECU under the passenger side dash with one from eBay, no difference. Same symptoms.
Tires are all same size and in good shape, and inflated to 30psi
Brakes are in good shape, no pulling, pads are good, rotors are not warped
Wheel bearings seem to be good, no play, no noise.
Suspension/steering components seem to be good, no play.

 

My $ says broken reluctor ring.

 

agree with carguy. I had same symptoms with a cracked ring.

 

Thanks guys, I have inspected the front two a couple times through the sensor hole and cleaned but even with close inspection don't see anything wrong with the fronts, when I tried to inspect the fears the little sensor bolt broke off so I stopped thinking to not make matters worse. With a bad ring shouldn't the wave form be messed even a little? How else would the computer know something is wrong?

 

In my case the first to fail was driver side rear. After removing the sensor I could move the ring a bit with my finger inserted through the hole. I guess the wave form was generally fine but if the ring moves independently of the axle sometimes it will think the brake has locked.

I broke one of those sensor bolts off on the driver side front. So annoying.

I disabled the ABS and haven't gotten around to fixing it since. Just ignoring the light. One thing I've learned is if all the other sensors fail the speedometer stops working along with some other weirdness.

 

jloogee,
i had similar problem. I would pull the rear axles and see which reluctor ring is broken. Mine had the passenger side ring broken. Not sure where in Minnesota you are but I took the axle to Proven Force in Brooklyn Park and got a new ring on for about $70.

I'd *not* recommend pulling the ABS sensors since they test ok and you may break them.

Not too tough. You will need a big socket set to remove the axle nut. A buddy had a harbor frieght set that worked fine.

 

Thanks for the info, I will try to get to it over the Thanksgiving weekend. I do live close to Brooklyn Center.

 

Thanks guys, finally got back to it and you were correct it was a cracked ring on the drivers side rear. Was not too hard to pull apart.

 

How do you check the abs on the 2002 with the dash light method?

 

Please avoid double posts. Your question has been answered in the other thread.

Salim