Climate Control Bug

Is this a failing 12v fault or a failing climate ecu issue?

Anyhow, what's wrong with celsius?

 

The Prius 12v is often said to have a normal useful life of about 5 years. Some do manage more than this, but the 12v is the cars achilles heel. It doesn't need to be as 'strong' as a traditional car as it doesn't need to crank the engine, but because it doesn't do that, it is hard to know when it is failing. In a traditional car you will notice the car gets slower to crank on a cold morning but with a Prius the 12v just keeps booting the computer up (which sends the signal to start the car) until one morning when it just doesn't quite have the power to do so. It can also cause all sorts of weird error messages and warning lights to be displayed when failing.

Often many weird problems are solved when the 12v is replaced, though sometimes the car could have more serious issues too. Replacing a 5+ year old 12v is a cheap fix and probably helpful even if it doesn't cure the issues. I'm not sure on the prices in the US (where you also get non Toyota alternatives to choose from), but here in the UK a genuine Toyota Prius 12v fitted by the dealer costs about £100 ($160) which includes our 20% sales tax.

 

Twiggy, have you reviewed the dealer service records for your car at Toyota Owners Official Website: Service Coupons, Owners Manuals, Service Scheduling and More ? If not, register the car. You may find record of a battery swap. Check the voltage of the 12v battery on the MFD:

Put vehicle in Ready or Acc mode (you may press EV to prevent the engine starting and wasting fuel if in Ready mode)
Hold down the "INFO-TEL" button on the NAV
Turn the headlamps on and off 4 times.
The diagnostic screen appears on the NAV.
On the first screen, press; "Function check/Setting"
then on the second: "Vehicle signal"
Battery voltage is the first on the list on the third screen that appears.
This shows the voltage under load in Ready or ACC mode
if you switch various things on/off you can see the voltage vary.
With no load when the battery had rested for a while mine showed 14.2v in ready mode
Switching the headlamps on it dropped to 10.4v, which shows how weak the battery capacity is. 10.4v would struggle to turn a starter motor on a conventional car. (from kithmo on toyotaownersclub)