Cruise Control would not set

[Roy124]

Corolla 2020, cruise control would not set yesterday.  Radar was fine and the speed limiter function worked. 

I thought a reboot might work.  Set off today and indeed the CC worked as expected. 

I don't know if it needed a long period power off or whether a simple power off/on would have worked. 

[Bernard Foy]

1 hour ago, Roy124 said:

Corolla 2020, cruise control would not set yesterday.  Radar was fine and the speed limiter function worked. 

I thought a reboot might work.  Set off today and indeed the CC worked as expected. 

I don't know if it needed a long period power off or whether a simple power off/on would have worked. 

It’s easy to confuse the setting up of the cruise control and the speed limit control, have another wee look at the handbook and try again 

[Roy124]

Oh Bernard, ye of little faith.  I think I know how it works. 

[Rambler56]

My ACC switched itself off today after about 10 minutes of driving.  Message said camera/radar not available.  Outside temp 10 degrees, no misting on windscreen, nothing obscuring screen on the outside.  The warning light went out after about 5 minutes and the ACC system was again available with no further problem.  A similar thing happened last week when the ACC made itself unavailable during a journey and reset after a restart.  Anyone else experiencing periodic dropout of ACC?  

[Roy124]

Rambler that sounds plausible.  I did a round trip at 4pm, ACC worked down but when we started the return leg is was probably directly into a low Sun.  After its initial failure I probably didn't try again. 

The camera would have been blinded and might be an essential component for ACC. 

[Rambler56]

17 hours ago, Roy124 said:

Rambler that sounds plausible.  I did a round trip at 4pm, ACC worked down but when we started the return leg is was probably directly into a low Sun.  After its initial failure I probably didn't try again. 

The camera would have been blinded and might be an essential component for ACC. 

The following information come from a guy in Texas (19AvHyXL on the Toyota Nation Forum) and goes into great detail about potential causes:

Radar Cruise Control Unavailable Clean Sensor:
- Millimeter wave radar sensor assembly becomes dirty

Radar Cruise Control Unavailable:

• Millimeter wave radar sensor assembly sensitivity reduced because of bad weather such as rain, fog, snow, or sandstorm
• Brake control by the dynamic radar cruise control system is temporarily unavailable
• The beam axis of the millimeter wave radar sensor assembly is being aligned
• The forward recognition camera is temporarily unavailable
• A system check is being performed after the engine has started

Here's some information on the site about the camera:
Forward recognition camera is mounted in the upper center of the windshield glass. The sensor detects vehicles and other objects on the road ahead using the image captured by the built-in monocular camera and determines their distance. With this, the recognition performance and reliability of the dynamic radar cruise control system has been enhanced.
FEATURES OF FORWARD RECOGNITION CAMERA
(a) The forward recognition camera has characteristics similar to those of human eyes. When the visibility is poor for the driver, the forward recognition camera may not properly detect lane markers or vehicles and objects on the road ahead.
(b) Only the objects in the forward recognition camera detection area can be detected.
(c) The forward recognition camera has a function to detect foreign matter in the area in front of the forward recognition camera.
HINT:
The forward recognition camera may not always detect dirt in the area in front of the forward recognition camera.
(d) In the following situations, the forward recognition camera may not detect objects such as a preceding vehicle, pedestrians or lane makers:
(1) When driving in inclement weather such as heavy rain or snow, dense fog, a sandstorm, etc.
(2) When the view of the forward recognition camera is obscured by steam, sand, smoke, water, snow or dust.
(3) When an intensely bright light, such as the sun or high beams of an oncoming vehicle shine directly into the forward recognition camera.
(4) When the surrounding area is dim, such as at dawn or dusk.
(5) When the headlights of the vehicle are turned off at night or in a tunnel.
(6) The contrast of the area around the vehicle is poor due to snow, etc.
(7) When the ambient temperature is low, the heater is operating with FOOT mode selected.
HINT:
If the upper area of the windshield glass fogs up, the system may not operate.
(e) In the following situations, the forward recognition camera may not detect objects appropriately:
(1) When the vehicle is being driven where a sudden change in brightness occurs, such as at the entrance or exit of a tunnel or in the shade.
(2) When the forward recognition camera is facing upward or downward due to inclination of the vehicle when overloaded.
(3) When the vehicle height is not standard due to modified suspension or non-standard tires.
(4) When the windshield glass is covered with water drops, snow, ice, dirt, frost, dust, oil, etc.
(5) When the windshield glass is fogged-up.
(6) When rain drops, washer fluid, or a wiper blade blocks the forward recognition camera.
(7) An object mounted on the Roof Rack is obstructing the area in front of the forward recognition camera.
(f) The front camera system may not operate properly in any of the following conditions:
(1) The forward recognition camera is misaligned or damaged due to a strong impact being applied to the camera or the area around it.
(2) The cabin temperature is extremely high.
(3) The cabin temperature is extremely low.
(4) Immediately after the engine is started.

[Roy124]

Rambler, thank you, that ticks several boxes in particular the low winter sun and dusk and dirt. 

Also confirmation that the system is multi sensor.  If you think about it, stationary road furniture could cause a radar system to stop the car dead.  The camera is necessary to aid discrimination.