B-Line

I've been getting a re-occuring warning light for the anti-lock brakes...
Thing is, it's not constant. I'd say maybe 15% of the time I drive the car, it triggers.
If I pull over and turn the car off and turn it back on, it generally (always) stays on. But the next day or two when I get back in the 993, it's almost always off.

Any thoughts on what's going on here? Thx.

ps- I guess considering how much time I spent racing cars without ABS, it doesn't frighten me all that much so I haven't really focused on because it's not constant.

Opo

Does it only do it when you start the car? Or while you are driving?

B-Line

Hmmmm, interesting question.

The more I think about it, the more I'm not sure. I wanna say that it happens just when I start the car but can't say for certain.
Cause I feel like today, it came on when I was already driving.

- What would it indicate if it came on while driving vs. startup?

01coccobet

could be a wheel speed sensor?
Did you wash the car lately?

B-Line

Hmmm, interesting... No, didn't wash but:

There is a spot every time I leave my neighborhood where there is a little stream of water in the road. The trail of water happens to be at this corkscrew left hand turn. Admittedly, I let the tires get wet then break the back end loose while shuffle steering/setting slip angle and throttling thru it. It's hella fun!

I think I noticed today, it went on shortly after I did that. That could make sense.

Is it possible the ABS system needs to be replaced?

Worst case scenario, what are we looking at?

Opo

The anti lock brake light used to come on in my c4 at cold start only, it use to stay on for about 30-45 seconds, I taught it was normal until I had my brakes bleed and than it stopped doing It, I don't know if it's because the brake fluid was dirty or what...

01coccobet

good starting point….

when was the last time you had a brake bleed and changed oil?

B-Line

It's been a while but used to have it routinely done when I was routinely tracking.

Why would that cause a malfunction though? The brakes don't feel like they need a bleed. I have plenty of pedal.

SC2993

I had the same thing happen and I was a little low on brake fluid. It was intermittent just like your scenario, turn off the car and then start up again, no light Topped it off and the light quit coming on, flushed the fluid not long after that and have not had the light come back on.

Mike J

With the C4 (and Turbo) there is a pump that needs to run that provides an assist for the braking circuit rather than the conventional vacuum assist - and that sometimes causes the anti-lock circuit light to trigger until enough pressure is built up, or at least from what I have observed.

I do not think the C2S uses a pump assist but cannot remember, it may depend on the brakes you have as well.

Cheer,

Mike

Magdaddy

ABS light, or brake pressure warning light...there's a difference. C4, C4S, and TT have the pump that Mike refers to. My car just started having the pressure warning light stay on for 7-10 seconds on initial start up, first thing-never on a restart.

My local P car tech says that's normal and acceptable. I'm planning of brake fluid change after my vacation, and road trip. My 90K will be here soon enough...

djantlive

My light comes on during a drive. I cleaned the ground straps for the ABS sensor. Where is the speed sensor? Is that the same as the ABS sensor on each wheel?

My fluid has been changed and the fluid is still high. Any idea? Would an OBD give any code?

01coccobet

IIRC ABS and speed sensor is the same thing

berni29

Hi

I had something similar on my 993, was the speed sensor. I do not know about 964's but it was a pig to remove. I have some advice if they are similar and yours is corroded into the hole.

Berni

djantlive

how would i find out which abs sensor is faulty?