Is it bad for your vehicle to leave cruise control on when going up or down inclines?
That’s the purpose of cruise control. To maintain a constant speed. My car has 115K, use cruise control extensively, many steep, high rise bridges, Hasn’t broken yet. Truck 55K, same.
I don’t even want to know why this question was asked. It isn’t like cruise control was developed last week.
Because some people don’t know! I thought this was the place to ask, not get reticuled!
CC is particularly helpful on downgrades as it will attempt to hold your speed by downshifting the transmission so you don’t have to ride your brakes, possibly overheating them. Old-school CC didn’t interact with the transmission so this is a significant step forward.
VOLVO_V70 is usually helpful but sometimes a bit grumpy, so don’t take it personally. It’s a reasonable question to ask here.
In some cars, on a steep uphill, the cruise control will lose speed and then shift and accelerate harshly to try to catch up, which could be a bit annoying. If that happens often, then you might choose to turn off the cruise control or just help it keep the speed up by adding some throttle yourself.
In addition to what NYBo says, there are also cars that will even apply the brakes on a downhill, though probably not many.
That is the exact way that the Cruise Control worked on my Taurus, and I found it to be extremely annoying. More than likely, the cruise control on my subsequent cars functioned better on upgrades, but ever since that Taurus, I have turned-off the Cruise Control on hills. I prefer to have more control over my car–including whether or not to downshift.