Open Road

I have a problem with the ABS system on my car.
When I put the brake, I can hear and feel the ABS engaging for maybe half a second but only at very low speed. Like when I get to maybe 3 miles an hour or so. No problem at all at cruising speed.
- The car needs to roll to a certain speed (maybe 5 miles an hour) to get this. If it stays at very low speed, no problem at all.
- I don't get any warning or light on the dash even when it's engaging.

I removed the ABS relay and no more problem. But of course I get the ABS light and warning...
It looks like one sensor feels like one wheel is locked (not turning) when it's turning at very low speed.

Could it be only a dirty sensor?

Or something else? Any hint?

Thanks in advance!

Bertrand Daoust wrote: ↑Mon May 08, 2023 6:10 pm I have a problem with the ABS system on my car.
When I put the brake, I can hear and feel the ABS engaging for maybe half a second but only at very low speed. Like when I get to maybe 3 miles an hour or so. No problem at all at cruising speed.
- The car needs to roll to a certain speed (maybe 5 miles an hour) to get this. If it stays at very low speed, no problem at all.
- I don't get any warning or light on the dash even when it's engaging.

I removed the ABS relay and no more problem. But of course I get the ABS light and warning...
It looks like one sensor feels like one wheel is locked (not turning) when it's turning at very low speed.

Could it be only a dirty sensor?

Or something else? Any hint?

Thanks in advance!

Sight unseen, my bet would be one (or more) wheel well ABS harnesses dying from age/exposure. Examine the harness and particularly the 8 plug connections. BUT…

First thing I’d do is plug in my Hammer and see if there are ABS codes.

@SeanR’s got the ABS diagnostic gizmo. He might have further ideas.

Thanks Dave.
What/where is that 8 plug connections?

Bertrand Daoust wrote: ↑Mon May 08, 2023 7:16 pm Thanks Dave.
What/where is that 8 plug connections?

two in spare tire well under plastic cover. one on each side of engine bay aft of shock towers. one on each wheel knuckle. one on each rear wheel carrier.

They are white (now brown with age) barrel-shaped bodies, about the size of two golf balls side-by-side. Each has three(*) two pin connectors. Each is secured by a black plastic retainer that “surrounds” the barrel-shaped body. The material of the bodies and connectors is twice as good as that for the knock, Hall, and CPS senders. Thus it lasts for about 30 years rather than 15 and then begins crumbling to dust.

Rubber retainer grommets for the wheel stub harnesses also degrade allowing the harnesses to wobble free, vibrate, and generally get messed up.

(*) ABS, brake pad warning, and RDK.

Locate a brake pad warning contact and trace it around a caliper until you see it terminate in what I describe above.

Perfect.
I'll take a look at all those.

Thanks again!

Almost all of the 928's I've driven have that little pulse when you start rolling. Not all of them, but most and it never comes back until the next start up and drive. It's like it is testing itself. If this is something that is going on continuously as you are driving from a stop, my first guess would be a relay in the pump faulting out. 2nd guess would be as worf says, signals getting confused from one of the sensors.

SeanR wrote: ↑Tue May 09, 2023 11:03 am Almost all of the 928's I've driven have that little pulse when you start rolling. Not all of them, but most and it never comes back until the next start up and drive. It's like it is testing itself.

This makes sense, but damned if I’ve ever noticed. I assume it’s due to the fact that 99.99% of my seat time is 5-speeds and something about the way I drive a 5-speed makes it very difficult to sense/provoke this self-test.

Thanks guys.

It looks to me that the signal is getting confused from one of the sensors.
Like one wheel is not turning while it is. Always at very low speed right before the car stops.
I need to go and clean all sensors I think...

A little follow up on this...

I cleaned 3 of the sensors and changed the rear driver's side (destroyed the old one when I removed it).
I also changed the battery this morning. The one I had was 10 years old and started to give me starting problem yesterday.
Now, everything is fine. No more ABS problem.
Is it cleaning the sensors (they were not very dirty) or the battery change that did the trick?
Can't say but everything's fine now!
Thanks.

Murphy’s cousin Serin Dipity would suggest that the actual problem was that the sensor you broke was already broken.

Nonetheless, glad you sorted it.