Transmission would not return to higher gear after descending a 10% grade with cruise control engaged

[slim]

We just returned from a vacation in Big Bend National Park. There are a couple locations where descents are 10 percent grades. Each time while going down hill in these locations with the cruise controlled engaged at 45 mph, the transmission would down-shift appropriately to maintain speed but then not upshift as the descent leveled out. RPMs were just above 3,000 RPM. You could feel the transmission attempt to upshift and the RPM needle twitch. I did not try to manually upshift while the cruise control was engaged. Pausing/cancelling cruise control allowed the transmission to return to normal operation. This anomaly repeated on five separate occasions. Because this anomaly occurred every time I descended in these two locations with cruise control engaged, I stopped using cruise control in these areas and relied on manually initiated downshifts and braking while in the Park. IMO, there is nothing mechanically wrong with the transmission and this may be related to programming that does not accommodate these conditions. No other transmission issues have occurred in the 14,000 miles logged since new, nor since we left the Park. I have previously used cruise control while descending but there has typically been a stop required at the bottom of the hill.

Has anyone else experienced this? I did not find any related technical bulletins. Kia Customer Service asked if I would go to the dealer to have the car checked for any fault codes which I am doing this morning. BTW, Kia Customer Service told me they do not handle any technical issues nor do they communicate with Kia Engineering. Everything technical has to go through the dealer. If anyone else has to report this issue you can reference my case number, #16237942.

 

[TellmeyourWHAT?]

We just returned from a vacation in Big Bend National Park. There are a couple locations where descents are 10 percent grades. Each time while going down hill in these locations with the cruise controlled engaged at 45 mph, the transmission would down-shift appropriately to maintain speed but then not upshift as the descent leveled out. RPMs were just above 3,000 RPM. You could feel the transmission attempt to upshift and the RPM needle twitch. I did not try to manually upshift while the cruise control was engaged. Pausing/cancelling cruise control allowed the transmission to return to normal operation. This anomaly repeated on five separate occasions. Because this anomaly occurred every time I descended in these two locations with cruise control engaged, I stopped using cruise control in these areas and relied on manually initiated downshifts and braking while in the Park. IMO, there is nothing mechanically wrong with the transmission and this may be related to programming that does not accommodate these conditions. No other transmission issues have occurred in the 14,000 miles logged since new, nor since we left the Park. I have previously used cruise control while descending but there has typically been a stop required at the bottom of the hill.

Has anyone else experienced this? I did not find any related technical bulletins. Kia Customer Service asked if I would go to the dealer to have the car checked for any fault codes which I am doing this morning. BTW, Kia Customer Service told me they do not handle any technical issues nor do they communicate with Kia Engineering. Everything technical has to go through the dealer. If anyone else has to report this issue you can reference my case number, #16237942.

Obviously something inherent in the CC. I find CC to be quirky at best.

 

[slim]

Tellme, you could be right that it was a cruise control issue vice a transmission issue. Regardless, I do not believe this is a mechanical issue, just something to do with programming, trans or CC. Its confusing when it occurs but easy to compensate for if you know what is happening, e.g., cancel then resume the CC and everything works as normal.

 

[slim]

The Kia dealer did a fault scan and found no codes (image below if you are interested in what the scan tool looks like). They said they were unable to report issues to Kia Engineering that could not be duplicated. Since there is no terrain like this locally, they just documented this anomaly in my file. One aspect they did bring up was about how the cruise control maintains speed in downhill situations, e.g, the use of throttle, down-shifting, and braking. They emphasized that they have seen use of CC in downhill situations cause excessive brake wear. They have had Tellurides operating in mountainous terrain needing their pads replaced at 40,000 miles. I need to pay attention more so I can determine when the CC is using the brakes and will be more cautious using CC to control speed in downhill situations.

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[Deb in Bailey]

For what it's worth, I live in the mountains of CO and have for over 20 years. I have lived where you have miles of down or up hill to get anywhere - everytime you leave your driveway.

I have had brakes last over over 100 K miles (yes!). How? Because I don't use my brakes. I use my transmission. I've never had a car that slowed me down when cruise control was set. I just downshift and brake as little as possible.

It has always driven me absolutely nuts when going down any hill (big or small, steep grade or not) and people are riding their brakes!

Yes, some of them are just unknowing drivers who are unaware of what they are doing to their brakes or how to use their manual gears. But I now realize that, these days, MANY of them are probably driving a car with the smart/adaptive cruise control like the Telly. And that cruise control is using the brakes ALL.THE.TIME.

It is the one thing that I highly dislike about the Telly. I love cruise control. I use it even on short trips and city driving. But I don't want my cruise control constantly braking - and it does, even on flat. Go downhill, and, yes, it might downshift, but it will brake too. One a slight hill, it will mostly brake and not downshift at all. On a steep decent, it may downshift, but your brakes are on constantly.

I have now learned that if I'm using cruise that I need to constantly watch my speed. As soon as my car ticks up just a bit higher than my set cruise, I hit the button to turn it off so my car doesn't brake. As soon as it drops just under my set speed, I hit the button to resume. Yup, I drive with my finger on that button and my eyes constantly looking at my speed (thank you heads-up display).

And if I am going down hill, I always use my manual gears to slow myself down. I sparingly use my brakes as needed.

I know this is not what your original question was about. I agree what you are experiencing is just the way things are. I've had similar things happen in other cars - sometimes the transmission just doesn't upshift when it could/should. Some sort of manual adjustment (releasing cruise, or manually shifting for a moment) resets everything.

But as for driving the Telly in the mountains or on any steep decline - turn off the cruise and drive yourself. Use your gears, not your brakes!

 

[slim]

Deb, my intention was to provide an informative thread, so your post is spot on. Thanks for sharing your experiences.

 

[Rocketdog]

Related cruise control issue? While towing our camper with CC engaged, when descending a grade the CC attempts to hold the speed set. While doing so I've experienced steering wheel shudder/vibration which goes away when I immediately disengage CC. Then yesterday when not towing, on a flat road and CC engaged at 70 mph all of a sudden the whole vehicle shudders. I immediately braked which disengaged the CC and the shudder went away. Turned on CC a bit after and everything is normal.

I've towed the camper over 10K miles and this anomaly just started and yesterday's event was scary.

 

[slim]

Rocketdog, I do not tow that often but I would first check to make sure this wasn't caused by a trailer issue, e.g., not enough tongue weight, weight imbalance in the trailer, a tire issue, etc.

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