F31 (320d Auto) Cruise Control Braking issue

[SeiW500]

Was driving along the motorway yesterday on Cruise Control and the car kept slowing down by approx 5mph then speeding back up to the set speed. I turned the Cruise Control off and stated driving to the throttle and the car kept wanting to slow down (as if the car was putting the brakes on!)
Anybody else had this issue?
I don't really want to drive the car at the moment until it's fixed but BMW want £85 to do diagnostic check & road test and i'm not sure if the car will repeat the problem on their test!
Andy

[steveinarizona]

ACC or regular cruise control?

[SeiW500]

No sure if ACC, the car breaks itself if you drop the cruise limit buy 5-10mph (in normal conditions) it’s now trying to do this on its own, even when cruise control is not activated. It only does it when it’s raining, even light rain. I suspect water ingress somewhere?

[911gone]

ACC would only do this if you were deemed to be too close to the vehicle in front of you, or if the sensor was dirty/impaired. Not sure when ACC was first available on the 3 series, but you should be able to see a sensor on the front bumper if it is fitted.

Braking to maintain speed with cruise on is standard function, so it does sound like you have a bit of a gremlin if this is what your car has.

[SeiW500]

Definitely NOT got ACC then....