Hello guys,

my friends 90 964 C2 has developed a strange problem with ABS

The light comes on occasionally, but not always
Yesterday the front wheels locked on the track, but the ABS light didnt trigger indicationg no problems.
All sensors were recently cleaned but no cure
Any ideas what can be wrong ?

 

It does that sometimes..I do not pay attention to the light anymore. Did the fronts lock under heavy breaking?

 

yes it did that under heavy breaking on the track
ABS Light was off

created a flat spot

 

Mine does this, too ... ABS light come on intermittently, usually after hitting rough spot in pavement at speed. Doesn't happen all the time; sometimes, doesn't happen for weeks, then it will happen every 10 minutes on a long drive.

Could someone please point out specific sensors, locations, etc., that need cleaning?

 

Can anyone confirm this for me? I had heard that the ABS system was under pressure, and needed to be charged, if the fluid was changed out. Is this true? If so, this could be your issue.

Just a thought,

Erik Johnson

 

My car allso has irratic abs.
Anyone ?

 

Richard I have exactly the same issue with my 1993 C2 that you have with yours, yesterday I drove 130 miles to a racing circuit and it did it once after hitting a rough spot in the pavement, it didn´t come on again nor in the circuit laps neither in the return trip.
It usually comes on in long trips never in short ones (less than 30 miles)
Unfortunately my mechanic was at the circuit with his notebook but didn´t have the right socket to plug in a 964 so we are still in the dark

 

Here's what I found when I had similar problems in my '90 C2:

For some reason Porsche uses a completly separate power lead for the ABS system which is terminated piggy-back fashion onto the main connector at the positive battery terminal (this is true for the '90 C2 but I'm not sure whether it is the same on all 964s). There are at least two potential problems with this setup that can lead to erratic ABS operation.

1. The ABS power teminal is held on by a small nut which can loosen over time leading to high resistance or open circuit.

2. Corrosion can form under the terminal (stray battery acid etc.) leading to a high resistance connection.

In either case the ABS circuit eventually can't get the juice it needs to operate and indicates a fault condition.

I cleaned it up and tightened the nut, everything has been fine since.

Jim G.

 

Sounds like good info from Jim. I've never heard of that one before.

The other known problem is a bad joint in the dash clock which can cause the ABS light to (falsely) illuminate. A low battery can also illuminate the ABS light.

 

Bear in mind that there are two levels of ABS fault alarms:

1. "Minor Fault" - ABS light on its own
2. "Major Fault" - ABS light and warning beeper noise

Regarding the solder joints in the clock: the while that may seem odd as a cause for an ABS alarm, what's really happening is the system iis monitoring the integrity of the warning lamp circuit ... if the bulb were burnt out (or missing), it could not illuminate to indicate a fault condition. Therefore, almost anything in the lamp circuit, including loose sockets or an intermittent filament can raise an alarm .

Further to C24FUN's note about the battery connection, there have been reports of similar faults caused by dodgy chassis ground connections near the ABS pump and ABS brain.

.. Gregg

 

To update: I recently removed the ABS relay, which appeared loose. I then brushed off the relay terminals, spread them apart ever so slightly, and reinserted. Quite frankly, the whole assembly still seemed a bit loose -- it would wiggle slightly when I jostled it -- but the ABS light hasn't come back on since.

 

Where is this abs power terminal?

I have been having erratic abs light (abs works fine).. Seems to go off more since it started raining.

 

Nice splitty !

 

In the first para:

"Porsche uses a completly separate power lead for the ABS system which is terminated piggy-back fashion onto the main connector at the positive battery terminal."

So this is in the front compartment on the cable clamp for the +12V battery connection.

Cheers!

Jim G.

 

I had the ABS light up on occasion at the track last year if I hit a rough spot/turtles/etc so, after disconnecting the battery, I took the connector off the ABS controller and sprayed both ABS controller connector and the plug with DeoxIt and then let it dry overnight - hopefully it will help!

Marc