Engine Brake Q...

I haven't driven my new Prius in the mountains yet but don't remember my Gen 2 doing that. It just started coasting until I hit the gas.

 

i have similar rxperience. i think the computer is just doing its thing and being extra smart

 

Yes, I'm told that's what it's designed to do to stop over-charging (and overheating) the battery. With Gen 4, "B MODE" is entered automatically going downhill after the battery is full. The kinetic energy from going downhill has to go somewhere once the battery is full, so it spins the engine, that's instead of wearing out the brakes.

There have been several threads on this.

 

No idea - just an idiosyncrasy - someone put a sophisticated metering on it, and I think came to the conclusion that it's in "limbo*" for a couple of minutes till the battery temperature stabilises after a rapid charge.

*limbo - a technical term which escapes my understanding.

 

That could be the case if the battery needs to cool further before safely charging. How long have you had the car? How many miles?

Is this a recent change? If so, check the hybrid fan vent on the lower rear passenger seat. The manual says to just vacuum the grille, but if you remove it you can see a filter in behind that too. If that vent gets clogged with pet hair or other debris, the cooling fan needs to work harder and traction battery can get too hot.

 

I tried checking mine when it first happened - and it was clean as a whistle, but check that nothing is over the vents. The main one is the one on the corner of the rear seat (left of the photo), we're not absolutely certain what the vent in the middle is (right in the photo), but I make sure it isn't covered.

 

Are you sure about this? I don't see it mentioned in the Owner's Manual. I think you still have to place the shift lever in "B" mode, it's not automatic...

 

When descending a hill with cruise control on, the prius will maintain the speed the cruise control is set at, the engine brake can be heard, I prefer to let the computer control my speed when going down hill, and uphill and on the flat.
The Gen2 manual warned about to much use of the (B) lever, I notice my Prime Advanced uses the engine brake frequently.
I prefer to maintain the speed limit.

 

The same thing happens with Gen 4, even if it could charge the battery. On my trip to work I turn off cruise on the small downhill and brake manually to recharge the battery instead of wasting the energy.

 

I looked after somebody else mentioned the filter behind. It is surprising the manual does not mention cleaning or replacing that. @Elektroingenieur is the cooling fan filter easily replaced on Gen 4?

 

I may be wrong but I don't believe the HV battery indicator is all that accurate TBH.

 

I suspect not too - particularly at the top of the range. It's just an indicator. Like the EV light which lags often.

Bear in mind that the battery WON'T go below about 20% and above 80% anyway, the HV indicator only theoretically utilises the area between. I've never noticed mine get as low as 1 bar, and only a couple of occasions has it got to the very top bar (after long downhill section).

 

The symptoms aren’t quite the same as those @Whiteyprius describes, but since he has a Prius Two with the NiMH battery, I wonder if it might be worth asking a dealer to do the HV ECU software update described in T-SB-0241-17, if it applies. This addresses other concerns “after repeated driving on long downhill slopes.”

It does—for MY 2017, pages 83, 88, 573–574, and 667.

Yes. The Owner’s Manual gives a procedure only for vacuuming the No. 1 HV battery intake filter in place, but removal is not difficult. The Repair Manual says to remove the battery service hole cover (a clip, then five claws) and the filter (a claw, then two more claws) and then clean the filter with compressed air or replace it. The part number is G92DH-47070; list price $11.35.

 

Australia obviously lacks the switchback dipping and winding roads of Cornwall!

 

Going downhill, when the battery gets full on my '19 awd-e the ICE starts to rev higher, but B-mode make it rev a lot higher.