So, does the system (both Mazda and others) handle engine braking differently when the car does it instead of the driver? I ask this as the vehicle (both my Mazda and my Jeep as well as the old Accord I put 300,000 miles on) will use engine braking when cruise control is operating and the car starts going down a long, steep hill that would cause the vehicle to exceed the set speed limit.

 

That's totally different. It applies only enough to slow the vehcle back to the set speed and shifts constantly during that process even if you don't always feel it. Unlike a person shift into a lower gear and holding it they to "engine brake. And if you are going down a mild hill it only shifts on gear lower but on some ECU programs if it is steep downhill can go 1-3 gears lower. Then if you were attentive the ECU programing is never as smooth to transmission back to no engine braking for a short distance. The algorithm is not near as efficient in some circumstances.

I suggest you cheat when you are known going downhill turn off complete your cruise control and actually drive the engine instead of relying on the ECU to adjust your down hill speeds. But that's just me.

Most owners that know this are generally the ones that tow and have a separate transmission temperature gauge which can confirm some aspects of my response. Your Mazda transmission is already operating at the same temperature as the engine coolant which does not make for a happy transmission in normal operations.
To long a downhill WILL super heat the transmission even letting the ECU adjust the transmission.

BTW I tuned that control off in my Mazda ECU. I got tired of the lag and how that effectively increases the use of gas which lowered your average MPG.

 

The Mazda CX‑5’s cruise control system does not actively use engine braking in the way that some older automatic transmissions with “manual” or “manual mode” could. The CX‑5’s Skyactiv automatic transmission is not designed for extended or frequent engine compression braking, which can cause transmission or torque converter issues over time.
The CX- 5 has:
1. Standard Cruise which may use engine braking on certain models and trims when going downhill.
2. Radar Cruise control (MRCC) with stop & go generally uses the brakes.
If engine braking is used in any vehicle, it is very doubtful any driver could match the engineered shifting that is programmed into the vehicles ECU.
You are best off letting a vehicle, if equipped for engine braking, to do the downshifting itself.

 

I didn't turn mine off. I like it. If I want to actively drive for the fun of it, I'll drive the MX5 with the six speed manual. However, just to clarify, I had the cruise set on 45 today and started down a long hill, about 2.5 miles. The transmission shifted from 6 to 4 and dropped to 3 a couple of times to maintain speed. At the bottom of the hill, it took the gears up to 6 again. It actually shifted just about the same as I would have had it not been on cruise.

Addressing Lobstah's comment, my CX5 GT doesn't have the adaptive cruise, only the regular, so I can't comment on that. On the Grand Cherokee, the adaptive cruise will use the 8 speed transmission first and fine tune it with the brakes. Of course, that car cost about twice as much as the CX5 so I would expect more advanced technology.

 

If you looked at a graph of gear selection ,torque ,engine speed and while some think they would shift the same as the ECU in cruise it not realistic .. It would be very difficult without a full set of monitors to adjust the drive-by-wire as accurate as the ECU and then if skilled and understanding the monitoring information only close.
Its really a personal choice, my only advise is that it is not good for the transmission. Average cost for a new Skyactiv transmission is 5000+ and almost 1000 labor .