Knut993TT

Since I bought my car some 8 years ago the speedometer has had a tendency to drop to 0 while driving normally down the street. It stays at 0 for 2-5 seconds, then jumps back to normal gain. During this period, the ABS & ABD light comes on. Until this spring, it only happended 2-3 times during a season and I considered it to be a minor issue. This year however, it happens all the time. I have a basic OBD-2 code reader, but it states there are no error codes.

I assume one of the wheel sensors is giving me some problem. Do I need a code reader with a particular feature to access this data?

tnx

Knut

trabi996

Seems like a ground issue to me.....

Barney1

Stop testing out the great brakes...... Just kidding... I've never heard of that..

Texas993

In a ferrari that was a sign that the alternator was going bad. Check your battery connections.

No power loss or change in engine performance?

Knut993TT

I will check the alternator and battery connections, just in case. However, other instruments and radio etc, operates well while the problem occurs. With regards to poor connectivity, there is no correlation with driving over rough vs smooth surfaces. Given the ABS & ABD light comes on, I assume the computer is detecting an input sensor issue and as a result disconnects the ABS circuits.

Trevor-uk

Hi Guys
I'm resurrecting this thread to see how and if the OP solved this or if anyone else has seen (and solved) this issue. It has just started to happen to my '96 C4S in the same manner - speedo drops to zero, ABS and ABD lights come on. I have noted that it can occur on uneven road. Speedo may spring back to life at any time while driving but warning lights stay on until ignition switched off and on again. No other driving or electrical function appears affected.

Is there a particular sensor that contributes both to the speedo signal and the ABS and ABD monitoring?

TIA

Trev

ScottMellor

Was the wiring harness recall done?

BHMav8r

Have you checked the fuse? Sometimes the leads that hold the fuse get spread apart and the circuit becomes intermitant, +1 on the battery connections - good luck.

Trevor-uk

Wiring harness recall done.

Battery connections and fuse to check - no.16?

Trevor-uk

Battery ok, voltage ok, fuse ok.
My research has pointed me towards the left rear wheel sensor as the source of the speedo signal (and contributor to ABD and ABS signals) - can anyone confirm this?
Is this a likely candidate for failure? I am unable to measure any difference statically from the others - around 1.75k ohm with some movement if the wheel is turned. Am I barking up the wrong tree?

Trev

chuaed

I'm experiencing the same issue with my speedo recently. Speedometer drops to zero on occasions with ABS and "!" light flashing intermittently.

Has anyone established the root cause of this fault recurrence?

Thanks
Ed.

Knut993TT

For my particular issue, i was able to narrow down the problem to rear driver wheel sensor. I replaced the sensor and years of agony was gone. Used a hairdryer to warm up one sensor at the time until the light came on in dash.

chuaed

Thanks, i will look into / replace the wheel sensors. Fingers crossed this solves the problem!

jarhed123

Bringing this post up again because I am having the same problem with my '99 996. The ABS light is on and the speedometer drops to 0 for a few seconds before coming back to life, and the cycle repeats itself. I would like to know which wheel sensor it was that you guys have been replacing. The only sensor I notice is the brake sensor. Thanks

ronnie993tt

Or you can do nothing, drive as fast as you want, blame it on the speedo when the tax collector stops you............