"P" abnormality in 2008 prius

It sounds like you could have a bad 12 volt. Run the test Weird stuff happening? MPGs dropping? Test The Battery | PriusChat after the car has sat MANY hours. Let us know the 3 voltages. Do not run out and change it until someone's given you feedback on the voltages.

 

You don't need a tool/volt-ohm meter. It's built into the car via the MFD... although we're not sure how accurate the voltage is on everyone's car.

We've found it useless to have the dealer "test" 12 volt batteries on the Prius. See Prius beeps after being turned off, then won't start | Page 2 | PriusChat. Can't you let it sit overnight and then run the test?

 

With the 12v battery being almost 5 years old, it would be a reasonable preventive measure to change it anyway. Almost time for key fob batteries as well.

 

I'll second that.

 

Hi jlstough. Are you sure that the Prius was "running" (ready mode) while you were parked? In ready mode it should keep the 12V battery charged from the DC-DC converter, and start/stop the engine as needed to maintain overall charge (on the big 200V battery).

Is it possible that you were instead just in "accessory" mode when this occurred? It would make what then happened not at all unlikely or unusual.

 

Yeah that would make sense. When it's in ready mode you'll see the (main) battery losing charge on the energy monitor display, and when it gets low the engine will automatically come on and charge it (and the cycle repeats). This however does no harm to the main battery as it's very much designed for these cycles, and the amount of gasoline used is very small (probably less than 20 cents worth per hour).

When you're in accessory mode then the main battery is not losing charge, but the 12V battery definitely is. Unfortunately the 12V battery doesn't handle deep discharge very well and is pretty easily to ruined by doing this too often. The bottom line is that you're much better off to let it waste a few cents worth of gas in ready mode compared to the few hundred dollars that the new 12V battery can cost. Personally I only use accessory mode if I'm sitting for less than 10 minutes. You could definitely go a lot longer if you knew for certain that the 12V battery was in top condition, but if at all uncertain then the 10 min limit seems to be a safe option.

 

If the engine coolant is running low check the water pump on the engine, look for pink deposits inside the pulley and in bad cases a line of deposit on the underside of the hood. If you can see any deposit the pump needs changing and the fluid replacing.

Use only Toyota SLLC coolant (super long life coolant) lasts for 120,000 miles, same coolant in the inverter tank in the center of the engine bay. Normally these do not need topping up. If the pump needs changing it is only the same job as any other car nothing special about it apart from getting all the air out of the system this can take time.

 

If the brake fluid is down from full but is above the low mark do not top it up or take the top off the container as this lets in moisture and dirt contaminating the fluid.

As the brake pads wear "and they wear very slowly on the Prius" the wear is taken up by the fluid and when the pads are replaced the fluid displaced will refill the container.

With normal driving expect between 100,000 to 250,000 miles to a set of brake pads.

 

Ditto the advice about leaving the car running, shifted to Park with the parking brake set. Listening to the radio would take days or weeks or burn a tank of gas, but it will kill the poor little 12V battery within a couple hours.

If you don't have an Owner's Manual for 2008 absolutely buy one and read it. It's full of info you need to know. Order a copy while you're at the dealer.

If you don't have the Scheduled Maintenance Guide (a Toyota document, not some dealer's), see here:
Toyota Parts and Service