Noise coming from back seat battery vent

I didn't notice the fan noise at all during the winter when I purchased the car, but started hearing the noise in Aug. It's very noticeable, and the outside temp doesn't matter. Sometimes it's on when the outside temp is below 70F and the fan is off. I believe it's totally unrelated to the fan controls. I don't see the problem as of now and I will do nothing.

Don't go to the dealer for diagnostic. They will most likely mess it up something or say nothings wrong. They are parts changers after all.

 

I've been monitoring fan speed with ScanGauge, seen it get up to a value of 4 (out of 6 I believe). Even then, I can't hear the fan. Maybe if the fan is noisy it's not so much the fan speed? Could be it needs cleaning, or?

 

I recently noticed this after having the dealer do a program upgrade. The fan seems to run almost all the time. This got me thinking (since the 2010) is about 4 years old an on the original 12V battery, I decided to check it. The battery (after sitting all night) was reading a mere 11.2 volts. Out came the battery tender and I let it go for an overnight charge. Checked and all was well with it reading 12.75 volts. The fan either seemed to run less or not as noticeable. All well for a little while, then I noticed the fan started running most of the time (I started driving the 2010 Prius, bought the wife a 2014 Prius and traded the 2008 in on it). I drive a pretty good distance and it has started getting cooler here, so I also thought, no problem with the fan running, it was taken care of. Not so, the fan started back with a vengeance (just last week) and I decided to check the battery once again. This time after sitting, it read 10.5 volts. Off to the local parts store to get one and replace it. So far this week (after replacing with an Optima), I have not heard the fan. I did make sure the Optima was fully charged prior to installing, so I should be good to go. It has been raining here most of the week, so it may not come on.....yet! I am wondering with the program upgrade, the tech having the door or doors open and installing the program upgrade, it ran the battery down even further and the system was attempting to charge the 12V battery causing more heat in the battery area, thus engaging the fan more often to cool. Not sure this is the smoking gun, but I'll keep an eye on it and check back later as to what my results are and if the fan comes back on.

 

If you have 10.5 volts then your battery is dead. Replace it now before it lets you down. You're about ready to replace at 4 years. Saying all this, I think mine needs to be replaced too. My mpg's are down for the first 10 miles if I haven't driven the car for a few days. I should practice what I preach.

 

Doesn't the Hybrid battery help charge your 12V battery? If it does than it certainly is working harder to charge your bad 12V so the fan works harder to cool it. Am I right?

 

Yes.

And running the car with a failed 12v puts extra stresses on the charging system.

 

Posts like THIS ONE are what makes PriusChat awesome!

 

I agree!!