ABS kicks in at slow speed all the time

[Nervous]

Here is another issue, pretty strange one.
First of all, I don't have ABS light on. I mean, it is ON when I turn key first time, but after that it disappears. So, it is good.
But seems to me ABS kicks on every time I slow down to about 1 mph. Even when I don't press brake pedal. So, if car slows down by itself at the time it is almost stopped I hear buzzing sound and if my foot is on brake pedal I feel pulsation, very slight one. Sometimes there is no pulsation at all, sometimes it is more pronounced than usually. Again - this happens always before full stop. No ABS light during kick in. Kinda weird, since on my Odyssey I never noticed anything like this (my other Camry doesn't have ABS). Any ideas where to look at?

[LynchburgCSI]

It might be a warped brake rotor or uneven pad wear rather than an ABS issue. Just something to think about and/or check out.

[Nervous]

Wrapped rotors are noticeable at high speed rather than at 1 mph... I want to disable ABS to check if issue disappears. Would it be enough to remove the ABS fuse?

[LynchburgCSI]

Ehhhh, warped rotors can be intermittent depending on pad wear. Trust me, I have 2 warped rotors on the truck right now (which is driving me NUTS). But anyways, I'd remove the fuse and check it out if I was you. Good idea.

edit: removing the fuse may cause the ABS light to come on. No worries though. The system will be off.

[Nervous]

Yeah, I'll try that. But I am sure this is ABS, since that sounds come even if I don't touch the brake pedal. You know, it looks like speed sensor(s) detect(s) that wheels are blocked, however they are not. Yeah and tires are fine, road is dry and speed is 1-5 mph.

[LynchburgCSI]

Could be a malfunctioning speed sensor sensor that the ABS ECU isn't picking up as "bad"... just "blocked". I agree with your theory there.

[Nervous]

Is there any way to test speed sensors? How do they work at all, btw?

[LynchburgCSI]

Originally Posted by Nervous

Is there any way to test speed sensors? How do they work at all, btw?

Not sure how they work. May just be a certain DC voltage for a certain amount of rotations. Grab a multimeter and the FSM?

[BMR]

I get the same thing sometimes; ABS kicking in at very low speeds, like when I'm almost stopped pulling into a parking spot. Particularly with the wheels turned. My ABS light is lit sometimes, it's got an intermittent fault. I get the faulty ABS kicking in when the ABS light is not lit.

I replaced one of the wheel speed sensors a while back, but the ABS system never has worked quite the way it should. I need to pull the code to verify, but I think the new sensor is bad. It's a Dorman mfd. part. If it checks bad, I'm gonna replace it with an OEM Toyota part.

[Nervous]

How exactly are you going to check if it is bad or not?

[73sport]

Think about this: The wheel speed sensors are reporting something to the ABS unit to make it happy. What is most likely is that one sensor has a metallic chunk stuck between its teeth making the ABS unit think that wheel is turning at reduced speed (its skidding when its not). Although painful, pull each of the sensors and clean them removing any foreign particles. I would also look through the port into the counter and spin each wheel repeatedly looking for foreign matter on the counter ring. There should be nothing on the counter ring.

^^ Granted, that all sounds good WHEN the brakes are applied. It seems very scary that the brakes are modulating themselves without pedal application. So this leads me to believe you have two faults. The switch feeding the ABS thinks the brakes are being applied. Check and adjust the switch!

Start reading the braking.pdf and its full of useful tips on troubleshooting this.

[73sport]

Originally Posted by Nervous

How exactly are you going to check if it is bad or not?

FRONT SPEED SENSOR AND SENSOR ROTOR SERRATIONS INSPECTION (REFERENCE)
INSPECT FRONT SPEED SENSOR AND SENSOR ROTOR SERRATIONS BY USING AN OSCILLO–
SCOPE
(a) Connect an oscilloscope to the speed sensor connector.
(b) Run the vehicle at 20 km/h (112.4 mph), and inspect speed sensor output wave.
(c) Check that C is 0.5 V or more. If not as specified, replace the speed sensor.
(d) Check that B is 30% or more of A.
If not as specified, replace the drive shaft.

Says you need an O'scope as it appears to put out a sign wave.


PS - you can check the other wheels at lower speeds of 12.4mph, but those front ones, 112.4mph ( or do they realy mean this>> 20km/h) haha!

Eitherway, ithe ABS ECU thinks they are OK - Clean them and I bet ONE part of your problem is solved!

Let us know!

[Nervous]

Yeah, I saw this and also laughed about 112 mph. Thanks, I'll try to clean everything up.

[73sport]

You have access to an O'scope?

[Nervous]

no, but could search for it if it would be really necessary.... Can multimeter be used somehow?