I am re-posting this here as this post might not have been noticed by many in the summary of proposed improvements. I have received 2 brief responses, but I thought I might try here, just in case it was not read by many. I observed an anomaly in the brakes of my Prius, and I would like to know if this is a characteristic of the Prius brake system, or if my car's brakes do not function properly. When driving at high speed, pressing the brake pedal first activates regen. Then, if you press more, eventually the mechanical brakes will engage. The more you press on the brake pedal, the more braking force is obtained. That is nicely done, as the transition is, in my opinion, subtle. However, when driving at low speed, the behaviour of the brake pedal is different. At low speed, there is barely any regen done, so pressing the brake pedal first does not do much. But then, as you press more, the mechanical brakes activate. The transition in this case is strong, as you go from "nearly no brake force" to "a lot more braking force". To me that feels strange, as the behaviour of the brake pedal will change depending on the speed. At high speed, the resulting brake force is relatively linear with respect to how much you press on the pedal. But at low speed, it is not: you press the pedal for a while during which not much happens. Then as the pedal reaches a certain distance along its course, a lot more braking force is obtained. That becomes worse when I drive on the highway, then take an exit: I press on the brake just a bit to slow the car down using regen, in anticipation for a stop sign. Then, when I reach a much lower speed, I start braking more if required. Sometimes, regen lowers my speed down to a point where regen does not slow the car down much any more. Then I press more on the brake. But since speed is low, I have to press a bit more than usual to reach the mechanical brake threshold. That feels like a "gap" in braking. I end up braking a lot at the last minute because of that gap. My wife always asks me why I am doing that. And all I did was to progressively press on the brake... Has anyone experienced that gap before? Perhaps I do not understand the brake system well enough. Or perhaps my brakes do not operate correctly. I am not sure. Any comments?
This is a good approach. Is this down to a stop or is there a minimum speed in this mode? The reason I ask is 19 mph (30 km/h) is a transition speed. I'm curious if the above happens when staying above this speed. This is a good approach. Can you define "low speed" in either km/h or mph? We need to understand the speeds involved as "low speed" and "high speed" are imprecise. Is this intermittent? If so, any rough estimate about what percent of times this happens? When we rented a 2001 Prius and test drove it in 2001, there was a brief, fleeting effect just as the car came to a stop at speeds under 5 mph (8 km/h.) By the time I bought our used, 2003 Prius, the effect was gone. The harder problem is finding out if your car has something special going on. Do you have a device with an accelerometer built-in? For example, an iPhone, iPad Touch, or other device with accelerometers and software to record and save the data? The reason I ask is if you can replicate the problem while recording the data, the device has to be taped or fixed to some part of the car, it can not be hand held, we can get engineering data to understand at least what the car is doing. This won't read out the the force applied to the brake pedal but it would let us understand: speed range - coming to a complete stop should be evidence and we can integrate the acceleration to plot the velocity profile Now there is one hypothesis, the brake signal light switch, that may be worth testing. I am not an expert in this area but several others have reported adjusting the brake light switch improves how cruise control kicks out when applying the brakes. Their symptom was that when on cruise control they had to apply significant brake force to disengaged cruise control. It is possible this may play a role in your symptoms. Certainly, any 'odds and ends' need to be eliminated. I have a recording accelerometer that can be used to measure what the vehicle is doing: We used this to document the 'brake pause' associated with the SSC-A0B fix. However, your description does not read like that problem but something different. The maintenance manual discusses a rather involved brake calibration procedure for the 2010 Prius (ZVW30.) But it isn't clear when this process is needed unless a major repair has been performed. I just don't know enough about Canadian laws and regulations about getting warranty work done on a perceived complaint. Bob Wilson
Bob, thank you very much for your post! I will get more data to support what I described. Thanks for suggesting the use of accelerometers... Our lab has 2 very accurate USB accelerometers (I wonder why I did not think of that). Do you know if OBD data provides info about how much a brake pedal is pressed?
"Now there is one hypothesis, the brake signal light switch, that may be worth testing. I am not an expert in this area but several others have reported adjusting the brake light switch improves how cruise control kicks out when applying the brakes. Their symptom was that when on cruise control they had to apply significant brake force to disengaged cruise control. It is possible this may play a role in your symptoms. Certainly, any 'odds and ends' need to be eliminated." This is the problem I'm having: the cruise control being reluctant to disengage unless the mechanical brakes are activated. I can brake with regen, ease off, and the Cruise will kick the speed back up. I've "fixed" it for now by pulling the Cruise lever back to disengage it at the same time I brake, but I'd like to get this fixed, as I use Cruise all the time.
[This is the problem I'm having: the cruise control being reluctant to disengage unless the mechanical brakes are activated. I can brake with regen, ease off, and the Cruise will kick the speed back up. I've "fixed" it for now by pulling the Cruise lever back to disengage it at the same time I brake, but I'd like to get this fixed, as I use Cruise all the time.[/QUOTE] I would have the switches adjusted. After reading posts on cruise and or brake light activation delays, I went out and checked mine. My brake lights illuminate almost instantly after pressing the pedal. There is probably less than a .25 inch of travel. Cruise dis-engagement occurs within same parameter. Don't know if the same switch operates both, but on my car they appear to happen with the same amount of pedal travel.
There are other threads on this - you can adjust when the computer detects the brakes being pressed, you do this by adjusting a green device under the dash. I've done it and the brake lights go on & CC goes off with just a feather of the brake. So I would recommend looking into that if you are good with your hands.
The easiest way to figure this out is just to goto a dealer and try out their Priuses. But from what you say, it sounds like something is off/needs to be adjusted, and it doesn't sound user-servicable either. The braking for my Prius is smooth, whether in regen, mech. braking, or even the transition. I can of course tell when its transitioning, but nothing should "kick in" - my braking is smooth at all speeds. Only when going under say 5-10 mph do I have to press just slightly more since regen does not work much at slow speeds (mech. braking takes over).
