Prius completely lost engine power *after* mountain pass

it might be that the refurb battery is weak and the engine was working too hard. i'm surprised you didn't get a trouble light though

 

Usually these symptoms happen with warning lights on the dash and those warming lights are stored as error codes so we can help you diagnose the problem. So... Did you have any warning lights? If you "lost all forward propulsion" it seems like you would?

 

battery protection mode, maybe?

 

Does your combination meter (the display that shows your speed, gear selection, and warning lights, among other things) work all the time or does it go dark from time to time?

 

Refurbed batteries are not noted for longevity. If the OP has Dr. Prius or some other method of reading the pack voltages it would be a good idea to check them.

That it failed after a long downhill suggests to me that the pack has problems accepting a large input current for a sustained period. One of the modules might have become very hot and the car shut down to protect it. When the car starts up do all the lights on the dash come on? As others have noted, it is hard to see how this didn't trigger a code and it should have turned on a warning light. On really long downhill runs it is prudent to shift to "B" and turn on the lights, A/C, defroster, and radio so that once the pack is fully charged the excess current has someplace to go other than the pack. That is how I configure our Prius when descending from the Grapevine, for instance. Before the pack is fully charged having all that stuff on reduces the rate it which it charges, which is easier on the modules.

Another possibility is that the pack fan is dirty and not moving enough air. That also could have resulted in the battery overheating when it was charging hard. If it has not been cleaned recently do so now.

This is really a long shot, but check the engine air filter. The car might have sucked in a swarm of bugs or bunch of small leaves or something like that. The could have blocked enough of the air flow that the car gave up, and when it stopped that stuff redistributed enough that it could breath again.

Edit: MFD -> dash

 

That's a steep, long climb. Mashing the pedal and whining out the engine isn't going to get you up that hill any faster. It's best to back-off and try to accelerate on the flats and short downhill sections to build up momentum for the next climb. Everybody is going to pass you and ride your bumper. Most likely your traction battery overheated. Make sure your traction battery fans are working and your cooling vents are clear. If your doing this trip a lot, install an engine coolant temperature gauge - so you don't blow up your motor.

Just my 2-cents..

If your going to keep this car; I'd install a new traction pack.

 

Verify that all the warning lights are visible (briefly) when the car starts up. There is a section in the user's manual that lists them all.

 

Certainly, it is an idea to use B for very long descents, but the other stuff is unnecessary. The car is clever enough to swap regen braking for greater engine braking when the battery is full. There is no excess current, so it doesn't need to go anywhere as the regen is switched off and replaced with old-fashioned engine braking to provide the requested braking effort. The hydraulic brakes continue to be used minimally.

 

I don't have confidence that the car dumps enough current into spinning the engine on a really long and steep downhill. On the steep grade going north down the Grapevine on I5 north of Los Angeles in "B", foot not on gas or brake, the car will accelerate due to gravity to unsafe speeds. Stepping on the brakes will invoke regen, and slow the car to a safe speed, but if the ICE motor spins faster to absorb that current I can't hear the difference. (There is no tachometer and that is much too dangerous a road to try to read a number like that off a cell phone while driving. Maybe next time I go that way and have a passenger with me.) So turning on all that other stuff is a (probably redundant) safety measure.

I also turn on the heat and open the windows going up that grade. Probably the car doesn't need that either, but as I inevitably pass cars and trucks going up the same grade which have overheated, it is another case of I would rather "pay for the insurance and not have to make a claim" than bet it all on the competence of the cooling system.

 

It doesn't do that. On a downhill, current is dumped into the battery until it is full. When the battery is full, current stops being dumped into the battery. To make up for the lost regen braking, the engine is configured as an air pump, and engine braking replaces regen braking. You add more or less braking with pedal pressure to control your speed.

Yes, until that battery is full. When the battery is full, engine braking takes over.

Then the battery is not full because, believe me, when the engine braking kicks in you will hear it.

Why would you think that to be the case? The engine would run cooler if anything.

 

Definitely, I hear that. What I meant is that when running down the slope in "B", foot not pressing on the brake pedal, and then the brake pedal is pressed, I do not hear any further change in the sound (already being) made by the ICE. Presumably it speeds up to create more engine braking when the pedal is pressed, but I cannot hear the difference. That said, my hearing is pretty poor these days, and I was always somewhat tone deaf, so if the frequency or volume only went up slightly I might not hear that change when somebody else could.

 

I don't know how the software handles engine braking in the old Prius, but on the Gen4 - If you engage your cruise control - the car will engine brake much sooner. It won't apply regular brakes if engine brakes isn't enough and also automatically brake if you approach another car too fast (radar detection). That's something I have to watch out for, I'm getting too used to cruise control automatically slowing the car in traffic. My car has run away on long steep slopes. Using B is the only way to control decent speeds w/o burning up the brakes by the time you reach the bottom of the mountain.

 

I don't think you do as I'm not talking about the normal engine pitch change when you engage B mode.

If that is the case, then the battery is not yet full because there is a definite engine roar change that correlates to the pressure input at the brake pedal.

Yes, sir, it definitely does. Deaf, or not, if you're not hearing the mighty engine roar the battery is not full because when it does engage, you can't miss it. In fact, it is so stark, that the first time it does happen to you, you have an oh sh1t3! moment and you scan the dash looking for warning lights.

FYI, the scenario being discussed is not the scenario you have described here.

Yes, the Gen 4 has more braking force in B than a Gen 2, but you won't be burning up the brakes in this scenario any time soon. People misjudge just how much braking force can be (and is) applied by the electric motors.

 

Naturally, there is a limit to how much power engine-twirling is able to dump. The limit is quite a bit less than the power rating of the engine as an engine.

As an engine, burning the fuel, the gen 2 engine specs out at 57 kW (or 76 HP) at 5000 RPM. But engine-twirling only runs it as a vacuum pump. The car isn't going to let it rev higher than 5000, and twirling 5000 as a vacuum pump maybe only dumps about 10 kW.

(That's not a number that's published in the manual. I measured my gen 3 being able to do just under 13 kW of braking by engine-twirling, but gen 3 has a slightly larger engine.)

If the grade of the descent and your speed work out to a larger amount of power than that, you will find yourself picking up speed, and having to use some friction braking to control it. That's just the nature of having more power coming at you from gravity than the engine can twirl away.

For those circumstances, I did read a study for truckers that came down in favor of periodically snubbing hard with the brakes, slowing down below your target speed, and then leaving them released until you have to snub again. They get real hot when you snub down, and it may work out to the same average amount of braking as riding them constantly, but the repeated snubbing/cooling turned out to have a slight advantage for condition of the brakes.

Because your descent power is a product of both the road grade and your speed, you can always slow down to reduce it, and if you go slow enough that the power is below what the engine can twirl off, then engine twirling will hold your speed and you won't have to use the brakes.

But, of course, sometimes that sweet speed could be slower than the people behind you want to go.

 

All the extra electric loads I mentioned provide that much more power margin before the physical brakes need to take the load.

On that particular road it is pretty common to see a truck on the side with its brakes smoking. I have seen a few literally on fire. There is a lot of energy involved in dropping thousands of feet of elevation in a few miles.

At 65 mph on that slope in "B" with the pack indicator solid green the car runs away. Thinking about your analysis, the situation becomes progressively worse as the car speeds up, at least until the car hits sufficient aerodynamic braking, probably around 90 mph or so. The cars are mostly going over 75 mph, some much faster. (Speed limit is 65.) The trucks have to crawl down at slower speeds because the speed limit for multi-axle vehicles is 45 or even 35 in some places. A few years ago Caltrans finally admitted that 55 mph was too fast for a heavy vehicle dropping 2600 ft. in 6 miles, and lowered the speed limit from 55. So yes, "B" alone might be sufficient if I slotted in between the trucks and stayed there all the way down the mountain. However, it makes me mighty nervous having a huge truck operating very near the limits of its brakes behind me on a steep slope. So I stay out with the cars and turn on the extra electrical loads. Doing it that way I only need to apply the brakes hard a few times on the way down. (On the way up I spend more time in with the trucks, because this Prius cannot fly up that hill like a lot of more powerful cars, and it is best to stay out of their way. Trucks crawling up a hill are not the same sort of danger as ones crawling down.)