3 quick beeps and engine shuts off

While driving, my 2004 Prius will randomly beep (3 quick beeps), then some of those times, the engine will shut off, the screen will switch to show the energy flow screen, and the car will drive on battery. It will run on battery until either the battery runs low or I press hard on the throttle, then the engine will turn back on.

Here's a video from my dashcam, from earlier today -

One of three scenarios usually occur:
1. I'm driving slowly (below the 41mph limit of the car's electric-only drive mode), and the three beeps cause the engine to shut off.
2. I'm driving above 41mph, and the three beeps doesn't cause the engine to shut off.
3. I'm driving above 41mph with cruise control on, and the three beeps causes the cruise control to disengage. The engine stays running, but I do have to re-engage the cruise control to resume my previously set speed.

I've been experiencing this since early this year, and while it has never caused any issues another than being annoying, I'm very curious to determine the cause. There are no codes thrown, and it is truly random - no temperature, speed, driving time, or other conditions seem to correlate.

Any idea what these 3 beeps indicate?

 

Great stuff guys, thanks for the info. I’ll address each question or point below:

From valde3:

• It also makes that sound when speed is bellow 41MPH?
  • Yes, speed does not seem to impact when or how often this issue happens.
• EV indicator is newer light?
  • I’m not sure what you mean here, is there a newer version of the EV indicator? My car doesn’t have an EV indicator per se, I can only tell if I’m driving in EV mode by sound, by the MPG indicator being maxed out, or by the energy flow screen showing energy only flowing the battery (and not the ICE).
• Multifunction display isn’t showing anything?
  • Nothing abnormal, no. I normally have the screen showing the MPG chart, and sometimes (oddly enough, not all the time) this beeping issue will cause the screen to switch over to the energy flow screen.
• Do you have ev-button kit installed?
  • No. I wonder sometimes if a previous owner did have it installed, and maybe there is some improperly removed component of it that is causing issues. Sounds unlikely, but I’m grasping at straws here.
• What did you check the codes with?
  • I have a cheapy $17 OBD scanner from Amazon that I use with both Dash and Torque on my phone. I also said that there are no codes because the check engine light does not turn on when this happens.

From Patrick Wong:

• Are you sure the sound is from the Prius and not from some other device in the car (like a phone, child's toy etc.)
  • Yes, positive.
• No warning lights on, or warning messages/icons on the MFD?
  • Correct, no warning lights or warning messages.
• Check the 12V battery voltage in the morning, after the car has been resting IG-OFF overnight.
  • Will do, what should I look for exactly? Probably worth noting that this issue has persisted across 3 different 12V batteries. I had the original battery that I bought the car with, replaced that with an Optima that failed, and then replaced that with a Toyota OEM battery that is in the car now (a few months old now).
• What is the fuel gauge level?
  • Varies, and doesn’t seem to correlate with this issue. The video I posted had the fuel gauge around the 1/4 mark.
• Check the engine oil level on the dipstick.
  • Sure, will do. Are you implying that there is an oil level sensor that would prevent the engine from running if the level drops?

From uart:

• as valde and Brit say, the only time I normally hear that rapid three beeps is when it either cant go into EV mode (via EV button) or when it kicks you out of EV mode for going too fast.
  • This is what I keep coming across as well, except that my car is a US model and doesn’t have an EV button or an explicit EV mode. I have wondered to myself quite a few times if there is some mistake or glitch in my car’s ECU.
• the message "EV mode is not currently available" on the MFD
  • Have never seen this on my car.
• check all the fluid levels and especially the inverter coolant pump as a matter of priority. I know that it can kick you out of cruise control if the inverter gets too hot.
  • Will do, good call. Are you thinking that inverter coolant pump overheating would effect the ICE operation?
• can you correlate these events at all with temperature (or how long and hard the car has been driven)?
  • Unfortunately not. It has happened on hot days and cold days, and on short drives as well as long drives. Seems to be truly random.

 

Fair guess, Bisco. Any idea how I could check to make sure? What is a coastal?

 

You might be on to something Bisco. Going through Coastal's site, I found their power outlet mod, which I believe my car has. My cigarette lighter stays on even when my car is off. So it is possible that a previous owner installed a Coastal EV mod as well. Very interesting!

 

I'm going to try holding my cruise control cancel for 2 seconds and see what happens!

 

Got in my car last night, it had been sitting for a while, so it was a cold start. While still in my parking spot, once the engine turned on, I held the cruise control cancel for a couple seconds. The engine continued to run, but I got the same 3 beeps! I repeated that a couple times, with the 3 beeps and the engine continuing to run each time.

Then I started driving, and it seemed like I was in EV mode for a bit - I was able to accelerate at a fairly normal pace without the engine turning on. At the next stop light, I accelerated a bit harder, and the engine did turn on accompanied by 3 beeps.

I was unable to get the car into EV mode for the rest of my 45 minute drive, although I did try a few times while on city streets. So it seems like my car may have the EV mod, and there is something wrong with the wiring. Maybe a loose connection.