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Why my Tata Altroz is behaving erratically when cruise control is on

This is my first car with cruise control. When I used this feature for the first time on my recent road trip, it felt scary.

BHPian GuyBurnsFuel recently shared this with other enthusiasts.

Hi, I am here to seek advice/suggestions/help.

I own a 2020 Altroz XT MT. I don't use cruise control often. On my recent road trip, I used it for the first time.

It was a scary experience. The RPM does seem to be fixed but the car feels like it accelerates for 2 seconds then coasts for another 2 seconds & so on. Is it normal for cruise control to behave like this?

Whenever I cruise on highways, I just keep a light foot & RPM remains stable maintaining a constant speed, it's very smooth but with cruise control, it feels scary.

Is everything alright? Do I need to get something checked from the service center? This is my first car with cruise control & honestly, I have not met many people who own a car with cruise control. Can someone help me with this?

Here's what BHPian Jeroen had to say about the matter:

Definitely not normal. A suggestion: did you check the owner's manual on how to operate the cruise control? Best check.

By and large all CCs more or less work the same.

There is a button that switches the CC on. Note, that means you can now start using the CC. Then there is a button to “set” the speed and engage the CC.

So with the CC switched on, driving at say 60 km/h you press set speed and the CC will maintain 60 km/h. When you drive downhill, it might slow down a bit.

But on a normal reasonably flat road it should hold a steady speed with no discernible hunting up and down as yours appear to be doing.

With the CC set, stepping on the brake or the clutch, the CC disengages, it remains on, but doesn’t control the speed anymore. On most CC there is a button that will allow you to “resume”. So you drive a steady 60 km/h with the CC on and speed set. You need to brake a bit, you slow down to say 50 km/h and hit the resume button. The CC will speed up your car until you drive 60km/h again.

Usually, there are also two buttons that allow you to increase or decrease the set speed. You will find very often that some of these functions are combined in several buttons and or stalk.

You need to drive at a certain minimum speed before the CC speed can be set. Your owner's manual will tell you. It is usually 30-40km/h, at a lower speed, you can’t set the CC speed, nor the resume function would work.

So better get it checked. Check with somebody who has an identical car.

Good luck, and let us know what you find.

Here's what BHPian narayans80 had to say about the matter:

I've used cruise control extensively on Corolla 4-speed AT and S-Cross MT in the last 5 years. There are subtle changes in rpm and speed depending on what sort of road you drive and to an extent the car's gear ratios.

My experience with respect to speed and rpm is as follows:

  • If you set the speed to say 80 or 81, the speed would subtly vary between 79 and 83 depending on the gradient. These are in GPS speed indicated by Google Maps/Sygic.
  • The RPM again would subtly vary depending on the gradient. I haven't looked too closely at the rpm meter. I expect 300-500 rpm.
  • In an AT (case in point of Corolla 4 speed AT), when you are on borderline gear ratio. This change in gradient will induce a downshift. This acceleration is violent.
  • In an MT, if you set the cruise control for 80. Had to slow down to 60, now press RES. This acceleration again would be violent. I usually reach closer/above the set speed and press RES.
  • If you have your leg on the accelerator (consciously or not). Cruise control will still be engaged. But there will be additional speed and corresponding rpm gain due to your accelerator inputs. Cruise control will disengage only if you press the clutch or brake.

Could you post the exact account of what rpm you observed and at what speed, what gear. This would paint a better picture of the behavior.

Here's what BHPian warrioraks had to say about the matter:

Doesn’t sound normal. The CC on my 2012 Honda City shows no such behaviour on flat roads. It’s a pretty smooth affair with no significant signs of acceleration or coasting.

However, acceleration or braking is apparent when the road has a steep incline (let’s say, going up a flyover or coming down).

You should get this checked.

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