Sudden unnecessary revving while downhill

It's not for no reason. When the hybrid drive can't dump energy into the battery (as would be normal while driving downhill) it is forced to prevent the production of excess electricity- so it forces the engine to spin instead of the motor-generator. In effect it is going into a variation of B mode for you.

That should normal up (along with all the other odd behaviors) once you have a new battery in.

 

Yeah there's been a few comments here, that the car will take it on itself to do some B-mode.

 

Is the battery meter full when this happens? If so, it is expected and desirable behavior. It revs for minor engine compression braking. Slightly pressing the gas pedal overrides the engine braking, slowing the engine.

In D mode, this behavior is similar to B mode but at a much lower level, e.g. just 2000 RPM in D, where B mode might hit 4600 RPM.

If the battery gauge is NOT showing full when this happens, then you have a real issue.

 

just another symptom of your battery dying.

 

i hope so too!

 

Normally when coasting or mild braking downhill, there will be some battery charging from regeneration, so the engine doesn't 'rev' or spin up. In D mode, only after the battery is full and can not longer accept any regeneration, will the engine 'rev' or spin up in its place.

As Bisco mentioned, this could also be a symptom of the battery capacity diminishing with age and wear, thus filling up quicker than when it was young.

 

it just happened to me today. i went down the hill and stopped at a red light. noticed battery completely full (I rarely see it). then ICE started when standing still for no reason. It happened to me only once before, don't remember the battery state back then.

 

It is normal for the Prius to use regeneration charging to rev the gas engine when the traction battery is already fully charged to prevent overcharging it. When the Prius is coasting, it is still producing regen charge by virtue of the forward motion, and it has to go somewhere. It is also normal for the car to continue to spin the gas motor when you come to a stop until the traction battery returns to a normal level. If you are experiencing this sort of engine revving, it is important to monitor the state of charge of the traction battery to confirm what is going on. Also, keep in mind there is no gas being burned, the electric motor is simply spinning the gas motor to burn off excess battery charge.

 

Did you get your new battery yet ???? I'm shopping and its like $1000 or $1900 at Hybrid Battery shop vs $5000 dealer

 

I've always wondered why my engine is roaring like that after coming down a steep hill. And I love looking at a full hybrid battery charge because the very last bar is always darker than the rest of the bars on the screen. Now I know. Carry on.

 

You do not want a refurbished battery. That is jus a failed battery repaired with modules from other failed batteries. @2k1Toaster here sells a kit of new cells for $1600 shipped which basically gives you a new battery. You can recoup part of the cost by selling your old modules.

 

which nobody wants

 

I have heard people buy and sell them on eBay.

 

I've heard they're just modules from failed batteries.