2017 Accord manual tranny cruise control
 

I am very glad I bought this car but wonder how does the cruise control work going downhill or down grade? You can feel it trying to maintain the set speed. But is the car applying the brakes or is it retarding the gas?
Love the cruise but just wondering how Honda has engineered it. Not as good as the cruise on either of my BMW's but so much better than the cruise on my Tundra.

I've been driving cars with manual transmissions and cruise control since the late 1970s and to the best of my knowledge, there has never been a version of cruise control which applied brakes. For cars with manual transmissions, all the cruise control can do is back off the throttle, if the downhill is too steep to maintain speed using engine braking alone, the car will accelerate.

As a side note, many cars with automatic transmissions and cruise control will downshift automatically to attempt to maintain speed.

On a car with stability-control or traction control, it already operates the brakes for those functions. So it's not much of a stretch to have the cruise-control programmed to operate the brakes. I'll have to try that on a long downhill sometime.

My understanding is it is a regulatory/safety issue. I'm like 95% certain no cars sold in the U.S. have the ability to brake to maintain speed due to heading down a long steep grade.

I tried it this morning in my 2010 and it doesn't use the brakes. I guess it would be bad if your car could overheat its brakes without you knowing it.