kdfwagen

So I purchased a 1990 964 c2 and the ABS light goes off with the buzzer almost every time I drive it (after about 2minutes).

When I went to buy the car the only warning indicator light that would go off was the Brake Pad warning light (worn pads). The previous owner took it in before I bought it and found the rear brake pads were toast and he replaced them accordingly. After he replaced the pads the brake pad indicator warning light never came on again, even through my ownership. However, now the ABS light comes on. The owner had taken in it before I bought it to check out the ABS light after he fixed the brake pad indicator light. The shop said no faults for the ABS came up on the diagnostic/hammer tool. The shop concluded that the ABS light had to do with the brake pad indicator sensors because they are interconnected and haven't been replaced in a long time. Are these systems interconnected at all? They seem to think that the brake pad warning indicators seem to be tripping the ABS system some how through faulty wiring or bad sensors. Should I even try buying new brake pad indicator sensors or would it be a waste of money?

I pulled the ABS speed sensors recently and cleaned them very well, however a couple of the ABS sensors seemed to have small chips in the end piece of the magnet. Would this trip the ABS system? Should I try replacing the brake pad warning sensors before the ABS sensors?

sorry for the long question.... thanks!

darth

they're independent of each other

kdfwagen

that's what I thought, just wanted to confirm the insanity.. The past owner is a very nice guy though and likes to help when he can (volunteered to pay for sensors if needed).

-Just found my abs unit's ground wasn't securely bolted down and had a bit of corrosion on it. Hopefully that fixes the problem...

darth

you'll likely need a hammer to deluminate the abs light

PNine64

My brake pad wear indicators were ok so I zipped tied them up out of the way so I didn't have to muck with them. If you are questioning their function you could always bypass them. Also, I got an ABS light and had to replace the relay (different symptoms). I had the warning light but also lost speed and wing function. Less than $100 bucks though.

kdfwagen

so after I cleaned the sensors I should use a hammer/diagnostic tool to clear the light? It goes on after about 30 seconds-1 minute of driving, but when I first start it up the abs light is off..

kdfwagen

which ABS sensor? one of the speed sensors? all 4 of them?

Thanks guys.

PNine64

Sorry...I meant relay...not sensor...I will fix my post.

darth

"so after I cleaned the sensors I should use a hammer/diagnostic tool to clear the light?" That's the only way I know how to clear it, but I also had the seatbelt light.

kdfwagen

So the light still comes on even after cleaning/tightening those connections. I also noticed that when I start the car and drive it for the first ~minute or so at slow speeds the brake pedal feels funny like there is air in the lines or something. There will also be a weird shuddering sound when I hit the brakes at low speeds during the first ~minute of driving, but than it goes away? what could this be? the sound seems to come from the front of the car.. not very loud but it is definitely brake related.

PNine64

Did you bypass the brake wear sensors (or get new) to ensure those are not causing an issue?

http://www.porsche964.nl/my964/sensors.php

kdfwagen

so I did bypass the brake pad sensors but the abs still goes off every time I drive it (go figure). I took it into a reputable shop to have it scanned for codes but they could not connect to the computer with the "Hammer" or the newer reader... What else should I look for?

C24FUN

Search for "ABS Woes" to find out what my problem turned out to be.

Jim

darth

Dear KDFwagen

Like I mentioned above the brake pad sensors and the ABS are independent of one another or in other words one has nothing to do with the other, so disabling the brake wear sensors, as expected, will not affect the ABS light from illuminating. To extinguish the ABS light it will be necessary to have the correct hammer version talk to the cumputer to reset it.

Bill

tbennett017

+1 on Darth's comments above. I am only guessing, but it sounds like your ABS computer is not getting the signals it wants during its diagnostic phase. Does your rear wing function correctly? (goes up at ~50 MPH and back down at ~5MPH - and the light goes off?)

Your response #10 above has me thinking it's the ABS having a problem functioning at low speed/early operation... FWIW

Are you sure you fixed the grounding issue? Are you sure you can't connect to the car with a Hammer or other diag tool? This doesn't make sense to me...