I know this thread started a few years ago but I've been having intermittent issues with the ACC as described by the
OP. And I've done a fair bit of reading on it and have found the same suggested remedies and tried them out, including replacing the buttons.
After this happening to me again just last weekend I played around with pressing the various buttons on the steering wheel and observed the following and have come to some conclusions of my own.
I believe that the issue is not the switches as I believe they are operational. The reason I believe this is by the fact that the Speed Limiter button works but, also, I noticed that when I pressed the ACC button and then pressed the Speed Limiter button it needed to be pressed at least one more time in order to, I believe, deactivate the ACC function first. What that means, to me, is that the ACC button actually works and it is in ACC mode BUT it hasn't registered with the sensor and displayed on the screen.
I also determined this by pressing the ACC button once, and then pressing it a second time (within a short space of time) and it deactivated the ACC and then I pressed the Speed Limiter button and it activated immediately on the first press.
Is my explanation of what I am getting at clear?
Thus, imo, it is not the buttons on the steering wheel. It may not be, should not be, the contacts (I also bought the contact cleaner and tried that with zero effect in my case).
After dealing with this issue on my car on and off (it seems to happen most frequently in very cold weather, eg every time I have driven to the Snowys) it will then, as if magically, reactivate itself a matter of hours, days or weeks later. And will work fine for weeks and months until one day it will not. There seems to be no real consistency to why it doesn't work except it definitely has failed me every time I have driven to a very cold climate. But it has happened in warmer temps, too, but far less frequently.
Thus, I believe that the ACC button is fine and it is something somewhere else in the system, eg the sensor.
Just thought I'd share this as it just happened to me a few days ago and yesterday the ACC came back on and works perfectly fine, as if it has no fault at all.
But if you have the same response issue as me then I think the issue is not the buttons on the steering wheel so save yourself the cost of replacing those and look for the real source. Which is what I am doing now and hoping a check of the sensor contacts will resolve the issue for me on a more permanent basis.
Cheers