Hi folks,
Any ideas on this?

Symptom:
Driving ~at speed across rough roads, the AWD led blinks on in front of the gear shift as normal. However, on a continued rough road, the awd system light and "brake" light come on in the dash and consistently blink. A restart seems to remedy the problem, until another batch of rough road really upsets the car and the process repeats.

Granted, it does take a fairly bad road to trigger this. Checked the easy part - brake fluid level is completely full after the pump has primed.

Thoughts?

 

Just a guess, but perhaps all the bumping is affecting the accelerometers. You could try cleaning them.

 

another guess: do you´ve enough brake-fluid inside.?!

 

I'm no expert on C4's but if everything suggested above checks out then check your wheel bearings by raising the wheel off the ground and grabbing the tire at the 3 and 9 o'clock postion, try to push/pull at these spots to see if there is any play in the bearing. Accessive play maybe affecting the speed sensor and in turn sending a false or intermitten signal to the computer. Also, the fact that it only happens on bumpy roads where vibrations are setup, check you're connections at the wheel speed sensor connectors.

Hope this helps
Bill

 

+1. That would be my first guess. Good luck.

 

Is this a new problem? Did it coincide with any change in tire size?

With the C4, the tire OD needs to be virtually the same front and rear (approx 25") or you will trigger the AWD light.

 

Thanks for the tips. This problem just appeared and doesn't coincide with any other changes, tires or otherwise. A flaky sensor/connection sounds like a good guess. Now I just need the ambient temp to come up so that I can take a look.

 

Find someone with a Bosch hammer or scantool and check for any error codes.

Ive had my C4 light the same warning lights and throw a few "implauseable signal" codes from the accelerometers during some very spirited mountain driving and AutoX's.

 

Sounds like bragging rights - I'm so fast my accelerometers only signal "implauseable".

 

I had (maybe have) exactly the same problem. Both warning lights came on all of a sudden and for about six months it would come on intermittently. Restarting the car would reset everything.

I had the mechanic check the error codes and he could find a conclusive code that would solve things.

At the end of last year I changed all the brakes and put new tires on.

Since then I have not had any warning lights come on. Its been a year now.

I think my problem may have either been low brake fluid (solved with a brake change), issues with the speed sensors at the wheels (the mechanic cleaned up everything while doing the brakes) or uneven tire sizes (fixed with new tires).