I have a 2003 Prius that I have had about 4 years. It has under 80,000 miles on it and I have the Ecrostech Scanner which I have had for about 3 years. For the time I have had the Ecrostech I have noticed times when the regenerative braking was not working when I would depress the brake pedal. I understand the regen does not work from about 7 mph and below but my system often does not work even when it is above that speed. Has anyone had this problem? I have not been able to force it into regen. It seems to have a mind of its own as in perhaps a faulty ecu. Any ideas? Paul
I think that regen is highly dependent on the SOC (state of charge) - when the HV ECU sees a braking request, it negotiates with the Battery ECU to decide how much regen is available (how much storage space is available in the battery). If you already have a full or mostly full battery, you may not get as much regen as you would if the battery has a lower SOC.
Is this something recently noticed? Over what interval? By route planning, I minimize regenerative braking so its loss would not be noticed. Is this regeneration loss from braking on level streets or descending hills? Do you have some quantitative numbers? Thanks, Bob Wilson
I think you've got a mix of information there. The 7mph limit of regeneration is applicable to the second-generation, 2004-2009, onwards. You have a first-generation car. One of the major changes in the second-generation was the reconfiguration of the brake system to allow much more regenerative braking, due to two factors: electronic control of friction braking, so the friction brake can be eliminated entirely; and an expanded range of regen due, I think, to the increased power-handling capability of MG2 (up to 50kW from 33kW) and the battery. On the first-generation car, the hydraulic brakes are brought in first, with regen being added - there's a modulator to reduce the hydraulic pressure to the front brake cylinders. With gentle braking, you may not get any regen at all. There's a good (though marketing-led) document from Toyota on the changes for THS-II (i.e. the second-gen Prius): http://www.toyota.co.jp/en/tech/environment/ths2/SpecialReports_12.pdf
Thanks Bob, I have seen this regen behavior over about 3 years. I thought perhaps it was standard behavior but have recently thought maybe not. I looked through the threads in Prius Chat and found none that addressed this issue. I live in the mountains of western North Carolina (we have the highest mountain in eastern US, Mt. Mitchell, which I live near) so I have lots of occasions to observe the braking patterns of the regen. Even if my soc is at a low point say 45%, the regen still sometimes does not kick in when I brake. The intermittent quality seems to be more frequent in the winter but it does happen quite regularly in warmer weather. This does of course effect my mpg though it does not seem to be out of line with others. In winter I get about 37-42 and in summer I get 44-48. Currently I have a reading on the screen of 50.9 in 956 miles. I do get better mileage on the highway than I do in the city driving which might indicate I do not recoup all of my regen when braking at lights in the city. I get even better mileage when I drive from my home near Mt. Mitchell. The 50.9 mpg above has two of those trips in it. I travel from about 2000 feet to about 5000 feet and back down when I travel on the Blue Ridge Parkway to Asheville. When I descend to Asheville my soc gets up to 80% even without braking and so I can get into gliding much of the way, maybe about 25 miles. How is the regen triggered. Is it a microswitch in the brake pedal system? Could that system be faulty?
Owch! Hills are heck on the traction battery. Do you have a laptop or RS-232 computer and serial cable to record data from the Graham scanner? What I'd like to suggest is: 1) fast polling 2) minimum battery temperature 3) maximum battery temperature 4) minimum module voltage 5) maximum module voltage 6) traction battery current Record the data on the laptop starting from an 'overnight' cold soak. My data indicates the traction battery gets warmer when force charged and this would provide some insights. It appears to come from the Hybrid Vehicle ECU. The Auto Enginuity has the ability to read out activity on the bus and I've seen a "commanded regen" request but I'm not sure which ECU issued it. I would expect the brake ECU sends it to the HV ECU that implements the regen operation. However, the Auto Enginuity does not have that level of detail in the current software. Bob Wilson
I believe I found the solution to this problem though I have no idea how it fixed it. I decided to get the brake pads and rotors changed on the front of the car. The thinest pad had worn to about 1/8 inch thick compostion material, the thickest was 1/4. Since I have made this change the regenerative braking seems to always be functioning properly now. I have had this problem for about 3 years that I know of. It would appear that even though the pads last a long time in the Prius it is necessary to change them when they get to a certain wear thickness. Toyota perhaps has a spec on this but obviously I was unaware of it. The fact that the pad and rotor change were purely mechanical and that they fixed the problem it begs the question how did the car know the pads were thin since I assume the regen braking is an electronic function?
The minimum pad thickness spec is 1 mm (11 mm when new). I'm wondering whether your car's problem might be that a caliper was sticking.
