mark964

So, if I hit a nasty bump (which occurs too often on these lousy roads), the ABS Indicator Light comes on briefly. Any ideas as to where I should start looking? I'm guessing that one of the wheel sensors has a less than ideal connection. What do you folks think?

Cheers,
Mark

jimq

C2 or C4? location?

dfinnegan

Interesting. Is this the indicator light on the lower center console where you are able to switch into 4-wheel low? I have that little yellow light flash when I hit bumps on the highway. I've only noticed it at night, but I expect it happens in daylight as well, but I've just not noticed it.

dfinnegan

Sorry, I was describing the PDAS control system and not the ABS.

dfinnegan

which is normal? both lights?

poorscheC2

Mark, I have a 1990 C2 with the exact same problem. After checking all the basic connections I decided to let the Porsche dealership give it a go. After several hours of diagnostics (a.k.a.$$$$) they told me it was a faulty brain. I find it hard to believe because the system acts normal (pulses brakes when wet ect..) however once a decent bump is hit the abs and the warning lights illuminate and the buzzer goes off. I did not have the $1300 brain replaced, just a bit too much money for me right now, also I figure I will eventually find the true fault. Let me know if you find anything out. Thanks, Steve

garrett376

It is common for the ground connection near the ABS valve block to be corroded - several times people have posted this intermittent problem, and solved it by unscrewing, cleaning, and reinstalling the various ground points in the front hood (there are three, I think). From memory reading those posts, it seems the ground closest to the ABS valve block (behind the battery) is the culprit.

C4 guys - if you want to see your PDAS functioning more easily, install the green PDAS bulb in your combination instrument...
https://rennlist.com/forums/964-forum/106325-green-pdas-activation-light-in-dash-gauge-how-activate.html

poorscheC2

Great advice, I will check those grounds and fluid level tomorrow. Mark964 there is also a ground that can be cleaned above the abs brain under the carpet, in the front hood right side of car.

poorscheC2

Mark964 Have you figured any thing out. I cleaned all my grounds and the fluid level is fine. Still have the same problem. Any other ideas? Thanks, Steve

HODY905

Check also to see if your speedometer is working. I had a situation where the ABS light was on and the speedometer was not working. The problem was a relay in the main fuse box location above the fuel tank. I forget the name of the rely but I think you can look in Adrian's book and find it.

C4porsche964

This is a total speculation on my part, but I'll throw it out there and see if someone can shoot it down. The main thing that happens when you hit a big bump is that the PDAS hydraulic valves are actuated in the differentials. Since these share the same hydraulic system with the brakes and clutch, it is possible you have a defective PDAS valve such that once actuated, your hydraulic system de-pressurizes, setting off the warning lights and alarm. Or, perhaps there is air in the system resulting in the same thing. Do your brakes and/or clutch get soft? I might try bleeding the system first to see if that fixes the problem.

Jerry

Jerry

C4porsche964

Oops, I was thinking you had a C4. I don't know if a C2 works the same way.

mark964

OK, so I diagnosed and fixed the problem. Turned out to be a bad connection on the under side of the central fuse/relay panel up front. Took a while to figure out, but I did. So, thanks again to all who responded to my plea.

Mark

poorscheC2

Mark, congrats on fixing your problem. Any tips on how to troubleshoot the problem? Thanks, Steve