Red triangle sometimes shows, sometimes not, when starting 2008

Check your 12v battery. It happens when the battery is low on charge or dying.

 

Run the test at Weird stuff happening? MPGs dropping? Test The Battery | PriusChat after the car has sat for many hours or overnight. Please tell us the 3 voltages.

Don't run out and change your 12 volt battery until you tell us.

 

The 12v battery is in the boot under the floor just in front of the passengers (for you in the US) side rear light.

The MFD is (multi function display) in the center of the dash. Follow the instructions in post 3 above high lighted in blue.

 

There is a jump point under the hood inside the black fuse box that can be used. The box has a lid and is located on the left of the inverter (looking from the driver seat). Press away from the headlight at the bottom of the box (the part that is close to the headlight) and it should come off. You can then check the battery voltage with a multimeter.

Alternately, use the display screen to check.

 

I wouldn't take it to the dealer to "check the 12 volt". In many cases, we've found their tests to be not only a waste of money, but also useless (sometimes claiming a bad battery is good). See Prius beeps after being turned off, then won't start | Page 2 | PriusChat. You're better off checking w/a volt-ohm meter and/or via the MFD.

It's real simple. Just go into ACC mode then hold down the INFO button while flicking the lights back and forth between off and the parking light position 3x. It's pretty obvious after that.

If using the volt-ohm meter, I would check the voltage of the at the battery (in the back), not via the jumping terminals. There could be a voltage drop between the back and front of the car. You can get cheap multimeters/volt-ohm meters are Fry's, Harbor Freight Tools or maybe a Home Depot or Lowe's. Radio Shack has them too, but I can't speak to pricing (at least their coin cell batteries are a ripoff).

What do you mean by "red car outline beeping"? Are you talking about the flashing red light in the car after the car's been turned off? If so, that's normal. It's always done that.

 

My car started throwing that RED exclamation point when my 12 volt battery was dipping below 11.2 upon start up.
My battery was doing great but after the wife drove it 3 weeks straight I got in to use it one day and saw that triangle upon start up. Pretty sure she left a light on all day at work and killed my very well cared for going on 6 years old original battery. But it just throws it for a second upon start up and does not log a code. But it means the 12 volt is done.

I put in a Optima Yellowtop.

 

Nah that's another symptom of a bad 12 volt. You can't reprogram anything on the mfd.

It was trying to warn you !!! lol...

 

As everyone said/advised, you are having a dead 12V battery. Change it.

 

Little bummed that you decided to incur the expense of towing it to the dealer. There is a jump-start point under the hood. You could have bought a portable jump-starter at any store and started the car for probably 1/4th or less the cost + you own a jump starter now to use with any vehicle you want.

I am sure any automotive store people would have helped you with the jump-start. Prius is very similar to jumping any other car, really.

 

^^^
Just be sure not to reverse the polarity. That could lead to blowing the inverter --> 4 digit price tag to replace.

 

Once started (made ready) the 12v battery can be completely removed from the Prius and it will run just fine.