Good day all. I have a couple of questions about the operation of the ACC in my 2009 xf 4.2 SC. I have been unable to deactivate the ACC, that is turn off the gap control in the car while driving but still using Cruise Control is this really the case it seems a little odd. The other question I had was concerning the use by the ACC system of the rear brakes, does anyone know if the brakes are applied everytime the gap control is activated or is throttle manipulation the first line and brake only used if a strong braking action is needed. I hope that makes some sense. What can I say I'm retired now and answering odd questions is how I spend my day

 

Yes - that's correct. On the current JLR models with ACC you can reduce down the gap and there is a 'no gap' setting that makes it work like traditional cruse control. On the XF and other models of your era that wasn't the case. There are four gap settings (controlled on the steering wheel controls) but no traditional cruise setting

Not sure that it operates rear brakes vs all brakes? But to answer your question in typical ACC operation even in 'follow mode' when it slows to another vehicle it doesn't use the brakes. If someone pulls in front of you, you change lanes behind someone slow, or cars slow down sharply then it will use brakes. But in typical driving it would be pretty rare. It judges relative speed and eases off the throttle to cruise in behind the other car / it's very smooth!