The rotors and pads are fine...the local mechamic changed a "bad" ABS sensor and the problem still exists ...when applying the brake -the pedal "electronocally pulsates"....ABS lights operating correctly...any thoughts?????

 

Rick, I really don't know what to say to be honest anytime in my life that I have felt pulsating when braking it is a warped rotor. you could try having them turned, but you have stated that they are fine, however how were they detemined to be fine? A warped rotor is hard to notice by a physical inspection. I guess checking the ABS control module???? However if ABS is causing your pulse, then there should be some sort of clicking sound you hear when braking, that is the noise that ABS systems make when they are engaging for harsh braking. I still bet on the rotors...but I am not sure. C'mon guys it's his first post, surely we can give him some ideas on what to do here.

 

well, I don`t normaly just change out parts,but if I were you I would either take them to a local shop that turns rotors,(dependeng on what kind of condition their in, i.e ever been turned before thickness of them etc.) or just put new pads and rotors on,and be done with it.I agree with smerre,from what your describing,it sounds like your rotors.Unless your mechanic put them on a brake lathe,(to turn the rotors) He would not be able to tell if they are warped or not.

 

Welcome to the Club. I agree on checking out the rotors. I hope he doesn't have a bad axle. Sometimes differing tire pressures can also make a difference here. I met someone down here the other day who had this issue and also suggested removing the battery and trying it again, but still haven't heard back (incidentally he was taking it into a local Lexus dealer here), but apparently Lexus had already cleaned and attempted to fix it.

 

Can you describe the symptoms some more? Is it a hard mechanical knocking (that you can hear as well as feel) when you apply the brakes - that would be the antilock system kicking in. You would also loose braking power (you could feel that too). If it's more of a vibration/shimmy that you can feel but not hear (especially when slowing down gradually on off ramps at 40-60mph - and you won't loose any braking power), then it sounds like a warped rotor. If you can't describe or diagnose the problem any more, have the runout on your rotors checked and make sure they are within spec.

When you say the ABS lights are "operating normally" are they flashing/lighting up when you feel the pulsation?

 

Your description of "electronocally pulsates" makes it sound like an ABS problem more than a warped rotor which would be more of a "shimmy" type of vibration. Do you know what ABS activation feels like? You may have experienced this sometime in the past on snow/ice or otherwise slippery surface. The first thing I would do is pull the ABS breaker and operate without ABS for a test. If your problem is gone, there is no need to waste time checking the rotors. If it is the ABS system the service manual has a very good section on troubleshooting ABS.

 

RX 300 - re: pulating Brake Pedal - This is a pulsating tapping of the pedal just like the ABS working if I were stopping on ice (i live near Boston...I know about ice...)...I appreciate the responses I got...and here's an update: My local mechanic removed the fuse/relay to deactivate the ABS -- and the problem stopped...and he used a volt tester ...and here I'm vague...to test the sensors on all 4 wheels ---found the right rear to be off...and put in a $200 part -new sensor...and it did NOT fix the problem...and incidently he didn't charge me....I have an appointment Monday with lexus - and I'm nervous......any advice is appreciated.

 

Well that is a horse of a different color.This sounds like a problem some where in the abs. system for sure.Does a light come on in the dash,when this occurs?

 

Hmmmm, been reading up on the ABS system, I don't know if your RX has traction control or not though. Could be the ABS Main Relay, ABS Solenoid, ABS Motor relay, ABS Actuator, or the ABS ECU I am guessing based on what I have been reading. I wish you luck, and let us know what the problem ends up being.....

 

If it's not the sensor, is most likely the ABS sensor ring which is part of the axle shaft. This won't be cheap.

 

Ha,ha,Is anything cheap for our cars?

 

Tire valve stem covers....got'em free, LOL

 

ABS wheel sensors send an AC sine wave voltage at a frequency (frequency based upon speed of the axle) to the ABS computer. ABS computer evaluates the frequency of each axle, and if one frequency is lower by a certain percentage than the other axles with the brakes on, the system actuates the ABS system. A few people have had this problem including me. I put a scope on each sensor, it appears the rear pass side sensor has a problem. I will replace and let you know the results

Duane

 

Thanks for the comment -- no lights come on when it happens. The ABS light works -- comes on when i start the car -- but then correctly goes off.

 

Thaks Mike -- I'll let you know -- my app't is on Monday -- 5/12