996 C4S ABS & PSM Light

[audi321]

Hi all. My ABS and PSM lights are coming on with the first press of the brakes each day (resets when ignition is switched off).

I'm a fair way from my Porsche dealer (70 miles) so wondered whether it was worth getting my local indie to deal with it.

Anyone any ideas as to the most likely cause?

Cheers

[Magic919]

Braking.

Wheel speed sensor would be possibility. Reading the error code would help.

[thegoose]

Double check your tyre pressures first. It's odd that it's only when the brakes are pressed that the lights come on - normally if a wheel speed sensor is at fault the lights will come on as soon as the car sees that it's not getting a reading from one wheel when the other 3 are turning ok.

I agree it would be useful to at least get an OBDII code reader on it - these can be bought for £20-30 from Euro Car Parts, also Amazon & Argos sell them, once you have one they're very useful for any car (from the late nineties on).

Another common cause of those lights is the MAF failing, but that usually manifests itself in the lights coming on after caning it, not under braking.

[KungFuPanda]

Could be a faulty MAF. I changed to a K&N filter which my C4S didn't like. The ABS and PSM lights came on until I changed back to the normal air filter.

[Crimp a Length!]

Just had similar issue, turned out to be the MAF.

[Pope]

My money's on Brake light switch. The system measures pressure and light switch input - if it sees one without the other then it will ping the lights on.

Replaced more switches than pressure sensors