When I start my car the master warning light comes on with all the other lights and then goes off with the other lights. It does not come back on while driving and there is no warning sound with it. This just start happening. It never came on with other lights when first starting it up. I have a 2009 Prius
The first suspect is the 12V battery, which may be weak. Check it, or put a battery tender on it to make sure it is charged. If it is original, it might be time to replace. Make sure the bolt to the chassis on the negative lead is tight.
or test it first, as nh7o suggests. you'd like to have 12.5 volts or better, after the car has been off for a few hours. you may also want to have the codes read by a dealer, or auto store.
Access the 12 volt battery in the right rear. The cca of the OE battery is 325, not very much and with the age of your vehicle, if original, it's time to replace. Always use the correct AGM battery in a Prius. Being located inside the vehicle it is necessary a AGM type battery is used. Critical that the battery is in good condition and able to hold a charge when vehicle is shut off. It is the only source of power when attempting to ready the Prius. If the voltage falls too low trying to start, the contactors will not close and the HV side of the system will not connect up. It will set codes in different modules for low voltage, a dead give away the 12 volt battery is on its' way out.
