IS 300F Sport cruise control

bestcover · July 31, 2017

Hi I bought a Sept 2016 IS 300F Sort in February from Lexus dealer. 6000 miles ex demo
Great drive but I noticed just after purchase that if I set cruise control just before going down a slope, it does not set. Absolutely fine driving on level ground or uphill.
Mentioned it to the dealer today when in for 10000 service and the reply was that none of the service engineers had come across it before and so took another 5 models out to test them and the problem replicated itself every time - so they thought it was a deliberate safety feature built in by Lexus.

They have raised it with Lexus but to be honest, it seems a crazy comment - any other IS300F Sort owners had the same or can comment?

Thanks

Tony

bestcover · July 31, 2017

SPORT not SORT!!!!

Flytvr · August 1, 2017

@bestcover, not sure, but maybe try posting in the IS forum?

NemesisUK · August 1, 2017

5 other models do the same, do not a fault as such.

When you say you engage cruise just before going down a slope, I presume you are on the flat? Can you describe exactly what it is you are doing when the function refuses to engage?

bestcover · August 1, 2017

Thanks - basically I engage cruise and it displays SET on the display - however, on going downhill, speed increases. So on one hill near my home on an A road with a 30mph limit and a camera sometimes half way down, I set the speed at 29 but by the time I reach the bottom of the hill, I am clocking 37mph. So despite cruise saying SET, it doesn't set.

Just can't understand the explanation of being a Lexus safety feature ?

NemesisUK · August 1, 2017

Which type of cruise control do you have? Is it the 'standard' cruise or the radar controlled cruise?

If it's the standard version the car cannot reduce speed, so as the car gathers speed on the descent it will simply go faster. The cruise is still SET and operational and once at the bottom of the hill and the car starts to slow, it will apply the throttle to keep the speed as set.

The radar controlled cruise can if I'm understanding it correctly, reduce the cars speed to match that of the car in front (detected by the radar) and apply brakes to bring the speed down. It would also be able to do this when the car gathers speed down hill.

ETA - just read the owner's handbook for my RC and there it states that even with Dynamic radar cruise speed may exceed that set when descending steep hills.

I think your car is behaving as designed, you may be expecting too much from the cruise function?

Edited August 1, 2017 by NemesisUK
Read Owner's handbook

bestcover · August 1, 2017

It is the standard cruise control - however on my previous 2 lexus (both CT200h) and before that 2 Jags, the cruise control kept the speed constant regardless of gradient. In the courtesy car yesterday (ct200h sport), I set the speed at the top of the hill at 29mph and it stayed at 29mph all the way down, behaving in exactly the same way as my previous 4 cars so I don't think I am expecting too much.

To my mind a cruise control is designed to keep the speed constant once set.

Flytvr · August 1, 2017

Oi @bestcover, when you buying an ISF? 😀

bestcover · August 1, 2017

It is an IS 300 F Sport

NemesisUK · August 1, 2017

2 hours ago, bestcover said:

It is the standard cruise control - however on my previous 2 lexus (both CT200h) and before that 2 Jags, the cruise control kept the speed constant regardless of gradient. In the courtesy car yesterday (ct200h sport), I set the speed at the top of the hill at 29mph and it stayed at 29mph all the way down, behaving in exactly the same way as my previous 4 cars so I don't think I am expecting too much.

To my mind a cruise control is designed to keep the speed constant once set.

But in your opening post you said you tried 5 other models and they all did the same as your car? Now you're saying you took out a courtesy car and it worked as you expected it should.... Curious.

The handbook clearly states cruise control will not maintain the set speed on a steep downhill gradient.

Only my CLS55 with radar cruise would use the brakes to keep the speed down. My C class with standard cruise didn't.

NemesisUK · August 1, 2017

16 minutes ago, bestcover said:

It is an IS 300 F Sport

Which is very much not an IS-F.

This thread is in the wrong sub-forum.....

FTBBCVoodoo · August 1, 2017

I didn't think you could set Cruise Control below 30mph (29mph as mentioned) regardless of gradient.

Gonna have to go and try it now.

I can confirm you can set it at 160 on an autobahn :-)

bestcover · August 1, 2017

Nemesis - no I said the Lexus garage tried 5 other cars out because they had never come across it before -

ColinBarber · August 1, 2017

I've found the cruise control on the IS300h to allow the vehicle to speed up when going down hill, all my previous Toyota/Lexus vehicles have managed to maintain a speed within 1 mph of the set speed. Happens at low or high speed.

It seems to be by design and I suspect it is to improve economy. It certainly isn't a 'safety' feature, that is just your dealer making things up.

bestcover · August 1, 2017

Thanks Colin

matt8 · August 1, 2017

I'm certain my Is300h F Sport slows down to set speed when going down a hill and exceeding set speed, whilst in cruise control mode.

When at a set speed and I accelerate for an overtake, the speed comes back down to set speed quickly.

bestcover · August 1, 2017

Thanks Matt - that's what I thought should happen ....but doesn't on mine. Do you fancy testing yours down a hill tomorrow and reporting back

Cheers

Tony

matt8 · August 1, 2017

I'll have a go and let you know how I get on!

rayaans · August 1, 2017

29 mph is too low for the cruise control to engage. I'm sure it needs to be over 30mph.

matt8 · August 1, 2017

Cruise control is usable from 25mph for me.

NemesisUK · August 1, 2017

From approx 25mph for me also.

From the handbook ...

Do not use cruise control in any of the following situations.
Doing so may result in loss of control and could cause an accident resulting in death or
serious injury.
● In heavy traffic
●On roads with sharp bends
● On winding roads
● On slippery roads, such as those covered with rain, ice or snow
●On steep hills
Vehicle speed may exceed the set speed when driving down a steep hill.
● During emergency towing

Rabbers · August 2, 2017

13 hours ago, matt8 said:

Cruise control is usable from 25mph for me.

12 hours ago, NemesisUK said:

From approx 25mph...

An almost exact conversion of 40kmh, which is the speed below which cruise control cannot be engaged and, similarly, is programmed to

disengage after deceleration.

NemesisUK · August 2, 2017

Further info regarding discontinuation of cruise function, point #1 is quite interesting, wonder under what circumstances that might happen?

■ Automatic cruise control cancelation
Cruise control is automatically canceled in any of the following situations.
● Actual vehicle speed falls more than approximately 16 km/h (10 mph) below the set
speed.
● Actual vehicle speed is below approximately 40 km/h (25 mph).
● VSC is activated.
● TRC is activated for a period of time.
● When the VSC or TRC system is turned off by pressing the VSC OFF switch.

Ian J. Parsley · August 2, 2017

I'm actually a little surprised there are any cars with "regular cruise" which do *not* increase speed when going down a hill. Regular cruise control only affects the "accelerator" (at least in its original form), so it is inevitable that on steep hills speed will increase if you do not hit the brake.

On my IS300h Lux, certainly speed increased on hills; notably one which was a 30 zone going sharply downhill (even with cruise on this went up to 40); and another a steep motorway incline where 70 soon became 80. It is actually helpful to turn the system off.

It may be possible that some new models have regular cruise which also affects the brake. The adaptive cruise control I now have in the NX does (so, on the aforementioned slopes, speed is more or less maintained).

(See a post I put up about a week ago on what cruise actually is.)