Porsche 968 Tachoausfall und Anzeige ABS-Leuchtet

  • Hi,


    I observed the following problem this morning: :eek:
    When the car is stationary and when I switch the contact on, without starting the engine, immediately the warning sign (!) and the ABS light come on and stay lighted.
    When I drive the car, these lights stay on and the Tacho does not work. Braking seems normal.
    Google talks about left front wheel ABS sensor, ABS fuse, ABS relay, frequency converter...
    ?:-( Where to start? ABS fuse is OK and pulling and re-inserting ABS relay did not change anything.

    968 Cabrio 1993, +160.000 km, no engine problems
    Honda Prelude 1992, 150 PS, +388.000 km, rusty, nears the end of life, still no mechanical troubles

  • It seems to be the Sensor.

    Seit dem ich einen 968er habe, weiß ich, was an einem Auto alles kaputt gehen kann.
    "Ein Auto ist erst dann schnell genug, wenn man morgens davor steht und Angst hat es aufzuschließen."
    (Walter Röhrl)

  • When I had a bad wheel sensor with my Honda Prelude, the ABS light came on only after driving a short distance.
    On starting the Honda without driving, the ABS light shortly came on and then went out. This is the ABS ECU being tested. Then, driving the car some meters, the ABS light came on again, permanently.
    So it seems the wheels have to turn in order for the ABS ECU to test the sensors? ?:-(
    With the 968, the ABS light is constantly on, when the contact key is turned, even without starting the engine.
    ?:-(

    968 Cabrio 1993, +160.000 km, no engine problems
    Honda Prelude 1992, 150 PS, +388.000 km, rusty, nears the end of life, still no mechanical troubles

  • It is most likely either the relay or one of the ABS-Sensors.
    If the warning light is triggered before you drive there should be a short in the sensor. This can be checked with a multimeter. Compare the resistance of all sensors. The sensors sit in ab aluminium part of the suspension and corrosion crushes them over the years.
    Get a fault code readout if possible, this will safe you a lot of time.


    Plugging and unplugging the ABS-Relay won't work. It is often a bad solder spot in the relay. The bad news is that these relays are expensive, but they can be repairs if you are skilled enough....

    Schocki :khat:


    1987 944 Turbo, R.I.P. :pop:
    1991 944 S2, Kobaltblau, verkauft :wink:
    1972 911 T Targa, Geminiblau aka "Shelley" :saint:
    1992 928 GTS, Amazonasgrün aka "Das Phantom" :evil:


    It's not the speed that kills you, it's the sudden stop :old:.

  • After about two weeks with main warning light (!) and ABS light on, and no tacho, suddenly while driving, all went back to normal. Until now, no more problems.
    Somewhere there is a bad contact that has fixed itself for the moment.
    Anyway, I have a spare left frontwheel ABS sensor waiting if neccessary.
    Best regards, Frans.

    968 Cabrio 1993, +160.000 km, no engine problems
    Honda Prelude 1992, 150 PS, +388.000 km, rusty, nears the end of life, still no mechanical troubles

  • Nun komme ich in deutscher Sprache hinzu.


    Dieses Aussetzen "Tachosignal 0 ,ABS leuchtet" verstehe ich wie folgt:


    Die Tachonadel zeigt 0 Km/h wärend der Fahrt. Zwangsläufig meldet ABS "Fehler" weil die Räder sich drehen, aber das Tachosignal 0 anzeigt.


    Ist das dann nicht ein mechanischer Fehler der Tachowelle?


    Wenn während der Fahrt der Tacho 0 anzeigt, verliert auch mein "Becker Indianapolis" seine "GPS" Position, weil das Radio an der Tachowelle Signale abgreift.


    Liege ich mit meiner Ansicht falsch?


    Gruß Alpinist


    P.S. Dieses Problem taucht bei mir ab und zu auf, aber es stellt sich auch von alleine wieder ab.

  • Hallo,
    sorry for my answer in English, my German writing simply is not good enough.
    I have a Becker Cascade 7944 installed, and when the tacho was not working, I also had no GPS function.
    The tacho signal for my Becker is connected directly to the tacho signal of the combi instrument, it uses the same electrical signal. As far as I can see, the tacho signal is a pure electrical signal taken from the left ABS frontwheel sensor, so no mechanics are involved!
    As I wrote earlier, this fault condition repaired itself, and for the moment everything is working O.K.
    I suspect a bad contact at the left frontwheel ABS connector, or the left frontwheel sensor itself.
    Next time the car is in for service, we will look at this.
    Best regards, Frans.

    968 Cabrio 1993, +160.000 km, no engine problems
    Honda Prelude 1992, 150 PS, +388.000 km, rusty, nears the end of life, still no mechanical troubles