Unable to reset to higher speed in DRCC

Once the system is engaged moving to stalk up then releasing moves it up 1 mph if you hold it it’ll continue to increase about 1 mile an hour per second or so moving the stock down decreases a speed 1 mph per Push or hold it and it’ll continue to take the speed down about 1 mph per second.

 

That's definitely how the prius does it in the 2 priusses I have owned -- if the cruise is already on, the same action as set changes the cruise target 1mph different from what it originally does. If you want to accelerate 10MPH, push up on the stock 10 times. (or disengage the CC, then accelerate, then set. (what a pain.

 

I'm pretty sure my gen 3 prius acted the same as my prime. Maybe it's a DRCC vs. CC issue as my Gen 3 had DRCC also.

 

I can't remember how my Gen3 with just regular CC worked, but on PRIME definitely, @schja01 gave you the right answer. Once set, push the stalk up will speed up, but down which is the set will decrease the speed. If you want to set at a new higher speed, you have to first cancel the DRCC by pulling the stalk and then set it at the new higher speed.

 

You can engage it without the radar dynamic function and it will work as normal Prius do. To engage in dumb mode press and hold the stalk button until the confirmation message is displayed.

 

How do you enable this option ? Via techstream ? I have a C-HR hybrid ( european version ) which does that 5 km/h increment and I would like to do the same on my Prime.
Thanks!

 

The Repair Manual (more info) doesn’t mention any customizable parameters for cruise control behavior.

The System Diagram page for the Dynamic Radar Cruise Control system says that the driving support ECU assembly receives a “Country specification information signal” from the main body ECU, which has different firmware for each destination country. I imagine this is how the large adjustment increment is determined (Owner’s Manual (PDF), page 397).

 

Cruise control on the Prime is a handfull too learn. I thought I had the good old stuck throttle issue. But after 6 mths. I finally mastered how it works, but it was a handful. You will master it in time. Just know how too turn it off! And another thing don't use it when you are in heavy trafic. You will like it once you get it. Check the manual and read it lots as it is confusing as well

Posted via the PriusChat mobile app.

 

What's more fun for me is that the speed set on the DRCC and the speedometer get out of sync. Very often I will have it set for 65 and the speedo will read 64 for a prolonged period. Then, bumping it up once gets the speedo to 66. I suspect there's some kind of internal rounding error converting kph to mph.

 

Mine does this, too, and I explained why in a previous posting.

 

The chance to do some science! Luckily it will be straightforward to test these hypotheses. We should observe distinctly different behavior depending on which hypothesis is correct. If it's due to hysteresis control, the phenomenon will be equally likely to occur at all possible speed settings. If it's due to unit conversion errors there will be some speed settings where it's more common than other speed settings.

A simple test would be to try the following DRCC speed settings and keep track of how often the car settles into cruising 1 mph below the set speed:

• 61 mph
• 62 mph

If it's hysteresis control measures 61 or 62 mph setting should make no difference in how often the car ends up cruising 1 mph below the set speed. However, if it's due to conversion error 61 mph will be approximately 3 times more likely to fall to 60 mph than 62 mph is to fall to 61 mph.

I had composed a very long explanation of why, but decided against it.

 

Interesting. Let us know what you find out. I currently have no occasion to use DRCC. I will not be able to do the experiment myself.

 

This explanation makes the most sense to me. And it applies to regular cruise just as much as DRCC. If the system tries to hold the speed too precisely, it'll burn a lot more fuel making frequent, abrupt throttle changes than the infrequent and gradual ones used it just keeping it close. Our speed controls and oven burners worked the same way in can making. So do house thermostats. In fact, we replaced our previous one because it was too precise for my taste and making the air conditioner cycle on & off too often. The new one lets you set that dead band. Less wear and tear on the compressor with fewer starts but longer runs.

Still, if I set the cruise for 60, it'll sometimes want to run at 59 and sometimes at 60, bit I don't think I've ever seen it want to run at 61. I suppose that it's just configured to be a little offset to the low side.