ABS Problem?

[gsmiller]

I just started having a strange braking issue with my 02 Boxster S that I think could be an ABS problem...

The other morning while I was backing down my driveway, the ABS warning light came on. I shut off the car and used my OBDII scanner to check for codes. There were none that it could read (I'm assuming I need the Porsche specific tool or Durametric for this) but I cleared everything with the tool and when I started the car the warning was gone.

Then I drove in to work and felt some very strange braking. While braking at speed (roughly 50-60 mph) the pedal felt really stiff, vibrated and the car pulled to the left. It was pretty freaky. The roads weren't slick and I wouldn't think the ABS would try to kick in under that driving condition but that's what it felt like (I brake for this corner routinely and have never felt the car do this). I couldn't get the brakes to act up at slower speeds but tested a couple times on straights at higher speeds and the brakes did the same weird thing. The ABS warning light never came back on though.

I read that a dying battery could cause ABS issues and I definitely think I have a dying battery for other reasons. I'm only driving the Boxster 1-2 times a week right now and it's been colder here in Seattle. The battery is a pretty generic looking one that came in the car and I think is on its last legs. I had a couple issues starting the car recently when it's been cold and I've neglected to put it on the battery tender.

I hooked my battery tender up to the car and fully charged the battery yesterday, disconnected it before I went to bed and drove the car again to work this morning. No more ABS warning light but I had the same weird pulsing/pulling brake issue at higher speeds. Any guesses or suggestions on what I could check? Could it still be a battery issue even though I charged it up (maybe its weak and not putting out the normal amount of juice)? Any advice would be greatly appreciated. Braking issues are pretty nerve-wracking...

[JFP in PA]

The "ghost" MIL ABS light that sometimes comes on when alternators or batteries are dying is just that, a false MIL that does not show any other symptoms. Your car sounds more like it is a real issue, possibly a wheel speed sensor.

Get the car scanned with a PIWIS or Durametric system, which will give you a read out of what is up, and in the future, do not clear any codes until they have all been read and recorded.

[Wayne 962]

I agree with JFP - probably a sensor problem. It may just be dirty. You may want to remove the wheel and remove the sensor and clean the trigger wheel and the sensor itself.

-Wayne

[gsmiller]

Thanks for the fast responses guys! I will take a look at the sensors next and I'll update what ends up coming of it here.

[gsmiller]

It looks like cleaning the sensors did the trick. Thanks for the great advice! Definitely saved me a lot of time and money, and I got to learn something about my brakes along the way.

My front left sensor had a noticeable amount of grime on the tip but all four were a bit dirty. Wiped them all off with a rag, reinstalled, and the car seems to brake like normal again. Also gave me a good opportunity to clean my wheels.

Thanks again!