Cruise control not activating

This is most often caused by a sticking or mis-adjusted brake light switch.
OR......by a left-foot braking habit of the driver.

Can you see a little light reflected off the back glass around the 3rd brake light when it is ON ?
If yes, have a look at it when the cruise doesn't set.

 

possible clock spring issue

 

That's an important distinction.....that I did not pick up on from your first post.

I think that problem likely would NOT be associated with the brake switch but you can test that easy enough.

 

if it is, be careful buying a new one. the chinese non oem have a high failure rate, and installation is a pain.

 

In addition to those, make sure the car is in 'D' gear, not in 'B'. This has snagged me a few times when I forgot to switch back after a hill.

 

You need to rule out clock spring cable and brake light switch.

Brake light switch.
Depress the brake pedal, the brake lights come on? Release the brake pedal, the brake lights go off? If yes to these two questions, your brake light switch is not the cause of the cruise control not working.

Clock Spring Cable.
Do the radio and AC steering wheel buttons work at all positions? A simple test is to park the car with the wheels pointing forward, and the steering wheel dead centered. Place a piece of tape at the very top of the steering wheel (this is your 12 o'clock position). Make care READY. Test all the steering wheel buttons (radio, AC, etc), at this 12 o'clock position. Do all the steering wheel button functions work? Move the steering wheel to 1 o'clock, and perform the steering wheel button test again. Go to 2 o'clock and test the buttons. Keep doing this at the other "hour" positions (3, 4, 5, 6), then go to 11, 10, 9, 8, 7, 6. A broken clock spring cable will reveal itself by intermittent operability of some or all the steering wheel buttons, at certain hour positions.

This post has some good pictures of the clock spring cable and why a broken clock spring causes problems.
2006 Prius clock spring (spiral cable) repair | PriusChat

If brake light switch and clock spring cable are working, it will be something else. But these two items are the most common culprits.

Remember these old proverbs: You get what you pay for. Penny wise, pound foolish.

FAKE clocksprings are available on crapbay (ebay) for $8-$30.
toyota prius clockspring | eBay
Genuine OEM Toyota part costs $220 from Camelback Toyota; your original clockspring lasted 14 years (depending on your vehicle production date).
2007 Toyota Prius Parts - Camelback Toyota Parts - Genuine OEM Parts - Free Shipping​

Many posts of people who were penny wise, pound foolish. Crapbay part failed soon after installation (~1year). Now these people have to redo their labor or pay for someone's labor AGAIN.

The clockspring connects your steering wheel airbag to the SRS/Airbag ECUs.
Read post #3: Be careful of counterfeit Clocksprings / Spiral Cables sold online | PriusChat

 

Right idea but things can be intermittent.
Absolutely, positively ruling something OUT as a cause based on only one test can sometimes be a mistake.

 

You missed:
A broken clock spring cable will reveal itself by intermittent operability of some or all the steering wheel buttons, at certain hour positions.

 

a broken clock spring works twice a day

 

OK, so what do you intend to do next ?

It seems to me that you now have good evidence (repeatable) of generally where the problem IS......and unless you are considering taking the steering wheel apart yourself and checking out the "clock spring" and looking for a broken wire or loose connection.......I suggest that a shop visit would be appropriate.

If you do that, don't cloud the issue with ALL of the gory details, just tell them that it doesn't work until you turn the wheel all the way in one direction......and that everything else seems to work. That should be all they need to know.

 

Mine hasn’t these same issues. It’s not working on the highway because it will only let me set the cruise when the steering wheel is in perfect alignment and my alignment seems to be a little off @ the steering wheel.

 

I have installed cruise control after market in my prius gen 2 today. It works fine engages and disengages properly but on pressing the on button word CRUISE does not appear on cluster screen no cruise icon or symbol although upon hitting on desired speed it works. My mechanic said that as it was base version with no cruise control thats why it doesnot shows icon

Posted via the PriusChat mobile app.

 

My 2005 Prius' factory cruise control hasn't worked for years. Except occasionally it works once. Less than 1% of the times I try it.

My brake lights work based on the reflection on a wall behind me. (I never left-foot brake.)
The buttons on my steering wheel work at all clock positions.

Does this data point to a diagnosis? If so how much would Art's Automotive charge to fix it (I'm not really up to anything that's not easy)?

 

In my other post, I have reported the problem in my Prius a out the 615 error code, I did techstream test and it shows something wrong with the speed sensor on both left hand and right hand. now I noticed the cruise control not turning on at all, but if I clear the error code with the little obdII scanner,I can turn on the CC but the cruise word is flashing on and off.... Speedometer reading the speed fine though.
CC word still flashing while driving but no operation.

 

Try looking at the break light switch
It has two independent switches built in
One controls the break lights and the other controls the cruise control. If the CC switch goes bad then it is possible that the CC won't engage and 'CRUISE' in instrument panel will only blink