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Hello all. Wondering if you guys could shed any light on a weird little gremlin that keeps popping up with my B6 S4. After approx. 20 mins of driving, ABS and Traction Control lights come on and stay on. So I cut power and turn it over again (at lights, for example) and continue driving... then same again. Rinse and repeat.

Friend of mine has software but awaiting cable... but in the meantime, any ideas would be greatly appreciated!

What tyres have you got, have you changed tyres recently? There is a general belief that the rolling radius of the tyres need to be within 3mm to prevent winding the centre diff up, probably worth swapping the tyres around to reduce the rolling radius difference to see if that makes any difference.

Hi, thanks for the reply.

Pilot Sport 2, 235/40 R18 Y 95 on all-corners about four weeks ago, as it happens. Standard Avus 18 wheels (Changed from Eagle F1s rear, Continentals front - the set-up when bought from dealer last year).

If all tyres are identically worn, or hardly worn at all in my case, then I think I'm right in assuming that the swap wouldn't make much difference?

Recently had KW V3s fitted and ride height dropped around 10mm from standard. Also Hotchkis ARBs front and rear... potential source of problems?

If the tyre wear is even on all 4 that counts that one out, suggest you should get it scanned for faults as it could be an ABS sensor is faulty, worth checking to see if any sensors may have been bashed when the tyres were changed. As this is lighting a warning lamp there will be a DTC logged in the ECU which will give more info, suggest you post in the DTC section of forum if you get a code with the associated fault description or check the ross tech wiki.

Yup, next step is a scan. Thanks for taking the time, appreciate it.

you're welcome, hope it gets sorted out.

I'm on V3s with Hotchkis ARBs (RS4 ver) and had no probs apart from the occassional self leveling headlight warning, always a false alarm though

I had exactly the same thing and bought a genuine vagcom set up. It turned out to be the brake pedal switch which cost £9.55 from Audi and took about 15 minutes to fit.
You deffo need to scan the car. Mine first threw up a fault code relating to the brake pressure sensor, but one possible explanation of that code is a brake pedal switch. Used the measuring blocks to see sensor was working and then reset everything. Did a few runs to get the fault up several times to make sure i didn't have a one-off anomally and then rescanned. Hey presto brake switch implausible signal was my only fault and lights never come on since - hope this helps.
If you are in the north west you are welcome to use my vagcom cable mate.

Simon

Interesting...

Is the break pedal switch fault an actual safety concern (i.e. should I be driving the car if I potentially have this problem) or just something to live with until it's sorted? Don't like to take my chances, especially with two little ones in the back.

I am in NW, but NW London. Should be getting hooked up soon but thank you for the offer.

No, not as long as your brake lights still work. It will not affect the operation of the brakes per se but you will NOT have ABS or traction control whilst those warning lights are on. As soon as the fault trips the lights they stay on even if it was an intermittent 'blip' and the lights are working fine etc.

Your prob may not even be the switch, but i would pray that it is coz a 10 quid fix is an unusually pleasant result!!

Was the brake pedal switch, all sorted. Thanks again.

Where is the brake switch located? for future reference.

Just under the brake pedal arm. It sits to the left of the arm up under the dashboard. You have to take off the right hand end panel of the dash (which justs clips on) then ubdo the bolt under there and the three others under the drivers side of the dash. The panel just clips out then.

The switch twists through 90 degs then pulls out and unplugs. 15 mins tops.