Prius gen 2 Death triangle randomly appears

Take a look at your hybrid battery fan plug in the back right rear quarter and see what you got We got a lot of corrosion there a complete pin missing something you can just jump the wire across the plug and solder and tape it in or whatever you want to do for connection and that should take care of that if that's what's the problem that's a pretty easy fix A lot of people here in the States have to do that because they catch it too late and then you can push that plug and the new connections you made further in to the body panel and it'll be out of the way of future leaks water whatever seems to work well here anyway we get quite the rainy season.

 

Your problem is not the hybrid battery fan connector. From your data that was collected, you have weak battery modules in block numbers 10 and 11. The battery modules should be replaced.

 

Error code P3021 indicates a malfunction in the 11th pair of cells of the high-voltage battery. The data you provided shows that the nearest pairs of cells have a large difference in voltage.

 

That's the wrong plug look above the black piece of ductwork coming out of the center of the white fan right above that elbow You see that white connector with the black tape wrapped around it that's the fan connector for the hybrid battery undo that tape and look at the ends where the wire goes into the white portion of the plug or receptacle You're looking for green flaky crust that builds up from battery leaking and that kind of thing or corrosion on the pins etc now pulled the plug apart or you can measure the The voltage going through the plug and coming out the other end Is that happening on and on and on this plug is a known trouble spot it looks like this one may have been dealt with before your car looks very clean in this area I don't see any traces of common water ingress hanging out in the 12 volt tray but I can't see really well in the 12 volt tray usually that will be rusty on the floor of the 12 volt tray indicating water has been there and the rubber plugs have never been pushed through on either side and they need to be.

 

Look at the data that you provided in post #1.

The battery block resistances for blocks #10 & 11 are in the 30s, and all the other battery blocks are in the 20s.

What is important is the voltage difference between the battery blocks during hard acceleration (high positive amperage) and hard regenerative braking (high negative amperage). Look at line #128 and you see that the highest battery block is #11 at 17.93 volts, and the lowest battery block is #9 at 17.39 volts. That is a voltage difference of 0.54 volts. The battery is seeing 95 amps of regenerative braking.

The four modules that make up block #10 and #11 are weak, and they need to be replaced.

Do another data run and try to make the red triangle (master warning) light come on. You will find that the voltage difference between the lowest and highest battery block to be even higher than the 0.54 volts seen in line #128.

If you have a scan tool that is capable of reading freeze frame data, you can look at the battery block voltages when the error code is activated. Then you can see exactly which battery block caused the trouble code, like the code P3021 (block #11) as noted in your post #1.