Porsche Enthusiasts Club Forum

Hello.

Really need some help. I have a 2001 996TT. For a while now, only at slow speeds just before it comes to a stop (mostly happens on a slight incline) the ABS feels like it's kicking in for no apparent reason. I can feel it through the brake pedal and hear it too. Other than that it stops just fine and oddly, if I am braking from speed, it never seems to happen.

I get ABS/PCM lights too.

My indy, who has been brilliant, checked the error code thrown up on the diagnostic computer. It read that there was a unexpected (or impossible - something like that) input from the front left wheel sensor under breaking. We have replaced the left wheel sensor which admittedly did look worn out. Problem came back. We also replaced the ABS unit/pump as it is one and the same. No joy.

The ABS and TC lights come on at the latter stages of every journey but not during braking; they seem to acknowledge a (the) fault. Once the car is turned off they disappear. They don't appear on start up (rarely they stay on) and the problem only really starts some time into a journey, usually after some urban driving where i guess the brakes are used more frequently.

The only other thing he can suggest is replacing the entire wiring loom which is a big job as their maybe a breach somewhere which throws up a bad input. I'm not convinced as he ran an impedance test which came up clean. For good measure we changed the brake light switch to no avail and checked the maff (in case of a secondary problem throwing up the warning lights) which is fine.

Tyre pressures and tyres all check out as OK.

Anyone ANY ideas on what else it could be?? It's driving me mad. Moreover, can anyone recommend anywhere who can remedy it? Should I go back to an OPC?

got to say, it looks like wiring to me too.
would it not be possible to just wire the sensor independent of the loom to the control input ?
would at least serve for diagnostics, and save replacing a rather expensive loom

Hi

Having has a lot of problems with the ABS on my 928, I have learnt a LOT about it...lol

The general rule is.....IF it happens while moving its the sensors or leads from the sensors... IF it happens at a standstill (before you move) its an electronic problem (relays, abs ecus wiring etc etc)

Sooo.... although it MIGHT be the wiring....if it came to a new loom which will be massively expensive, personally I would change each wheel sensor one at a time first....

All the best Brett

Hi, I have a 996 TT of the same year with the same sounding problem, have a look at the condition of the ABS surface on the outer CV joint, you may find it is quite broken up due to rust!

Been struggling with mine for awhile now, just changed the F\right speed sensor ,whata swine that old sensor was to get out?!

So I had the same after 4201 "Implausible signal" this can be debris in the toothed wheel,a cracked or chipped tooth, or as said earlier a wiring fault.

You need to unplug the ABS plug & with a multi meter test the power through the pinouts.

On mine It was the wiring to the right side & it was at the point where the loom went over the steering column, over the years it became brittle & with chaffing of the column it cracked the wires, when cold it made a contact but when it warmed up the contact was broken?!
Good luck though
John