ABS Pulse ????

[Cobra04]

Friend of mine has a 1994 Accord that right before the brake pedal bottoms out(end of stroke), he can hear what appears to be the ABS kicking in. He says it(pedal) slips a little bit and for a brief second he can now feel the abs(pulsate)working. This is under a NO SKID situation.

Anyone have any idea what could be the issue here ? Sensors ? ABS unit itself ?

Unplug sensors maybe and see if it still happens. This would then for sure indicate that it is either a sensor or the entire unit ?

thoughts ?

Thank-you

[jeffcoslacker]

I don't understand the problem...that's how ABS works....are you saying that it does this under normal braking?

[jeffcoslacker]

I'm a little dense this morning...that must be what you mean...If one wheel sensor reading is out of step with the others, even when NOT braking, it should see that as a problem and DISABLE the ABS system and set the ABS warning light....so it doesn't sound like a wheel speed sensor fault...

I could only see unwanted ABS operation without wheelslip if either the logic unit was going insane, or there was some mechanical problem cauing the physical relation between the sensor and the reluctor to change when the brakes are applied...but I can't think of a condition that would cause that, without seeing how the parts are mounted on it...

[Cobra04]

Originally Posted by jeffcoslacker

I don't understand the problem...that's how ABS works....are you saying that it does this under normal braking?

As stated in my first post. This is occuring in a NON SKID situation. It happens EVERYtime he steps on the brake. So in other words the ABS is kicking in(Somewhat) EACH and EVERYTIME he applies the brakes when in fact it SHOULD NOT be happening

[somick]

How do you know that the pulsation your friend feels is caused by ABS? Could it be just a warped rotors?

What is the speed of the vehicle when he applies brakes? The ABS system gets engaged by several factors. Or rather a combination of factors. One of the factors is vehicle's speed. Does he feel the pulsation at low speeds too?

Sam

[jeffcoslacker]

I was thinking some more about this...sorry for misunderstanding the problem originally...I would have just said I've got this car with ABS activating at the bottom of the pedal stroke under normal braking....

I'd forget the ABS and take a good look at the brakes first, to make sure there isn't some mechanical explanation that's causing a wheel to try to lock and drag under normal braking...like a broken return spring on a rear drum brake, or a leaking wheel cylinder with saturated brake shoes, something like that, just to verify and rule that out before you end up chasing your tail trying to find an ABS fault that may not even exist...it might be doing exactly what it's meant to do...just for the wrong reasons...

[Cobra04]

My buddy went ahead and disconnected both front sensors and the problem went away. ABS light is now on for obvious reasons. So what does this now mean ?

He also wants to know if he can plug just ONE sensor back in to see if problem comes back or do BOTH of them have to be plugged in.

Thanks

[Cobra04]

Originally Posted by Cobra04

My buddy went ahead and disconnected both front sensors and the problem went away. ABS light is now on for obvious reasons. So what does this now mean ?

He also wants to know if he can plug just ONE sensor back in to see if problem comes back or do BOTH of them have to be plugged in.

Thanks

Bump, Bump

[Cobra04]

Bump, Bump Bump

[jeffcoslacker]

Originally Posted by Cobra04

My buddy went ahead and disconnected both front sensors and the problem went away. ABS light is now on for obvious reasons. So what does this now mean ?

He also wants to know if he can plug just ONE sensor back in to see if problem comes back or do BOTH of them have to be plugged in.

Thanks

As long as one sensor is unplugged and not providing a signal, the ABS system is disabled...so it doesn't really mean that he's found anything useful, just that he's managed to disable the ABS. You won't be able to tell anything by doing this.

[jeffcoslacker]

Actually, though, you have proven that the problem is definitely in the ABS system, and not being caused by a mechanical problem with the brakes themselves, as I wondered about earlier....you'd have a wheel trying to lock up now if that were an issue..