A 2011 Prius with 189K miles on it and using 'B' mode on a long descent caused it to make a loud, medium pitch screeching / metal against metal grating type of noise. Was in Glacier National Park , "Going to the Sun Road", traveling west (from Logan Pass Visitor Center) downhill, switched to 'B' Mode on the descent. Speed modulated between 22 and 30 mph. On reaching "The Loop" close to Crystal Point (about 12 miles from where 'B' mode was engaged), the engine or transmission (was not in a position to stop and isolate the noise), starting making the above noise. The only way to stop the noise was to take the car of out 'B' mode and put into 'D' mode. I was able to replicate the above situation pretty accurately on two different days. Car did run / drive fine without incident after switching to 'D' mode, though I did not use 'B' mode for at least half an hour after the above incidents. Since then I have traveled another 3000+ miles (down to Moab, Canyonlands, Mesa Verde) and have not had any driveability or noise issues when using 'B' mode on the Interstate or State Hwys. However, none of the Interstate or State Hwy downhill sections are more than a few miles. Questions: Is there a mileage limit for which 'B' mode was designed or is there something else going on ? What may be the source of that noise ? Thank you.
It might be helpful for you to post a recording of the sound. B mode will produce some engine noise on a descent, increasing when the battery reaches full charge and increasing with the steepness of the descent, and subsiding if you shift from B to D. So pretty much all of that matches what you've described, except most of us don't hear it as a screeching or metal grating noise. That's why hearing the recording would help. We'd either be able to say "oh, yeah, that's the same sound ours makes", or "schezbzflat! that's really unusual!".
When was the last full brake inspection? Do you know roughly how many mm's there are on your current pads?
Thanks for your comments. Instead of replying to each one maybe I list my responses here: I am familiar with the noise the engine makes when in 'B' . It was not that noise. Think of gears grinding / clashing noise. Difficult to take a recording of the sound under the circumstances (if you are familiar with the "Going to the Sun Road": traffic, curves, incline). 'B' mode was perfect to descend to this road and keep within the speed limit while still being able to take in the views. Engine made it's usual 'B' mode (you are killing me whine) until around the 11 or 12 mile marker when the grinding / grating / clashing noise started. Fortunately I was able to replicate that on two different days . I was not riding the brakes and foot was not on the brake pedal. At 180K was the last full inspection (at Toyota dealership) and brake pads were not an issue . (If I recall I had quite a ways to go on the pads remaining) Transmission fluid was changed at 150K and no issues were reported then. All work done at Toyota Dealership only. I am wondering if something in the engine / drivetrain heats up in 'B' mode after 11 or 12 miles of use or if 'B' mode was not designed for usage of such continuous distance?
the only thing i have read is that b mode is exactly for conditions like that. we have lots of members who live in very mountainous areas, and i don't recall ever reading anything like this. if something is wrong with your drivetrain, you'll find out soon enough. in the meantime i would still get a thorough brake inspection, and check the tranny oil level. when was the last time you changed it?
From various online and topo sources: Logan Pass: elevation 6647 feet "The Loop" elevation ~4300 feet Distance: 8 miles (from VC, not actual road summit) descent: ~2350 feet average slope: ~6% (from summit, not VC) That amount of descent is a very normal use of B mode. If you were simply coasting down a winding road in B mode at a leisurely 22 to 30 mph, rather than barreling down a steeper major highway at 60 mph as I commonly do, then your overall mechanical and electrical and thermal stresses are significantly reduced. So while this is a significant amount of stress, I'd don't believe that you exceeded any mileage or total descent design limit. Or if you did, many of us often do worse.
Here is something to hope for. Perhaps you have a loose exhaust shield that reached a resonant frequency, assisted by a cold exhaust due to the long descent and ICE pumping air. I don't think anything could go haywire in the PSD (Prius "transmission") and still allow you to drive it back to California.
Thanks all. Car returned from dealership yesterday and they could not find anything of issue. Called them and gave them some of the suggestions from Priuschat and they could not find anything. I have a trip to Anchorage coming up next in this old car and fingers crossed. (At least its not terribly cold this time of year) Unrelated to priuschat, but if outdoors is your thing, I highly recommend a visit to Glacier National Park (aka, the Crown of the Continent) and any car with engine braking is a perfect vehicle to help you safely get around while enjoying the gorgeous area. Not sure what my experience would have been if I was in a car where I had to constantly ride my brakes.
All cars have engine braking. Some form of downshift is a federal requirement. Merely riding the brake, without appropriate downshifting, is a recipe for overheated brakes, and brake fade on the old-fashioned drum brakes. The Pikes Peak road even has a mandatory checkpoint where the attendant measures brake temperature with a remote IR thermometer gun. Not that the IR gun is really necessary, the vehicles that really need to pull into the 30 minute cooling off parking zone are already emitting quite a bit of stench and smoke.
