When does HV Bat cooling fan come on 2004

I think many people never hear their battery fan come on, although it does run at a very quiet slow speed often enough. It will only run on high under real heat stress. If you drive mainly on the highway, use the A/C, and do not encounter much in the way of big hills, then it will go unnoticed. If, after years, you do hear it, it means battery trouble is brewing, due to the internal resistance of the cells rising, or due to the fan being clogged with dust, hair, etc.

 

I put a piece of filter material (intended for vacuum cleaner motor filter) in the fan inlet on our 3rd gen, soon after purchase, about 18 months back. FWIW, I've never heard our fan, but periodic checking of that filter shows it's picked up a few things, a bug or two and some lint. So I'd assume the fan's running, just not audible.

 

i never heard my 04 or 08. i think you're climate has something to do with it as well.

 

Any time you get a nice hot summer day and a reasonably long drive, at the end of your trip I guaranty it will be running. Leave the Prius in ready and (with all other fans off, engine off, radio off etc) get out of the car and walk around to the right back door. Place your ear right next to the vent and you'll hear it running. It's whisper quiet on low speed, you really need your ear right there at the vent to hear it.

 

That's easy enough to check. Have you had a look to see if the inverter coolant is circulating in the reservoir yet?

 

It's worth a look because it's apparently common not to get all the air out of the coolant loop after replacing the pump. A week after mine was replaced the same warnings re-appeared; the cause was just trapped air.

In eight years in Dallas I've never noticed the battery fan running, so don't panic about never having heard it.

 

Very true, for 7 years, I never heard mine.

 

You must have turbulance in the pump AND bleed the air out, if it is not turbulent.