badger-100

Hi
Car: 996 C4 Cabriolet 1999 3.4l
This has been an ongoing problem for sometime, first it was rare but now its constant, so any thoughts would be gratefully received.
The symptom is that when driving with the PSM on you turn the steering wheel and the abs brakes come on. Turn off the PSM the abs brakes come on when turning the wheel and applying the brakes. When moving at low speed under 5mph all is ok.
I've changed the steering loom and the steering angle sensor which stopped the intermittent problem for a few months, but now its constant.
Any Ideas??
Thanks Mark

Slakker

What tires are you running and what size are they?

Sneaky Pete

Good point.....if your tire sizes are wonky that could make for some strange behaviors.

Badger...you a cheesehead?

5CHN3LL

I would guess that there is a problem with the sensor for one of the front wheels; the signal isn't correct and PSM is interpreting it as wheel slip and trying to correct for it.

Even with PSM "off," it is still monitoring for situations when the brakes are applied and there is wheel slippage; it will intervene at times when the brakes are applied even when the PSM Off button is illuminated. This is the one condition (brakes applied) where PSM is active even when you've disabled it using the switch.

A wonky tire size (front/rear mismatch) might cause issues with a C4's viscous coupling, and varying significantly from factory sizes will make the speedo inaccurate, but I don't know how it would cause PSM to do what OP described.

badger-100

Thanks guys for the responses, Sneaky Pete not sure about the Cheesehead comment, although I do like some Stilton occasionally!
The tyres are different, fronts are 225/40/ZR18 continental sports contact 2, rears are 265/35/ZR18 Hankook Ventus, although the problem was there before the tyres were changed.
5CHN3LL's idea about the front wheel sensor makes sense, I'll take them out and at least clean them. Also French roads (I'm not French by the way!!!) aren't the smoothest in places, which may have upset things

Sneaky Pete

Your moniker made me think you were from Wisconsin...the Badger State which is my home State. Also known as the Dairy State. With Dairy comes cheese and very good cheese too. Wisconsinites are also born Green Bay Packer fans.......us Packer fans like to drink beer, eat brats and cheese curds. After too many beers, brats and curds we don our cheese wedge hats......hence....wait for it.....we are called Cheeseheads. A picture for reference.

badger-100

Ahhhh Now I understand, you learn something everyday. I'm a Brit, we too like beer, sausages and cheese, although we usually refrain from wearing them on our heads, of course except on weekends! Never been to Wisconsin, but hope to one day, even only to sample the beer.

5CHN3LL

By my math, your front/rear size variance is within tolerance for the 996. Hopefully the issue is just with the wheel sensors and not anything more expensive that the sensors connect to...

badger-100

Thanks for the maths 5CHN3LL, time to get my hands dirty! I'll let you know how it goes!