Most often it's about the scan tool you used to try to read the DTC. Not all generic scan tools are able to show you the DTCs that cause the triangle to light. Toyota Techstream on a Windows laptop definitely can, and so can some of the alternatives reviewed in this thread: Gen2 OBD2 app review | PriusChat TL;DR the Autel MaxiAP 200 is a choice that gets a lot of love in that thread. If the triangle only flickers briefly as you swing around corners, check the engine oil.
What app are you using? Or is it an old handheld device? Also you can have problems triggering a red triangle for the brakes that won't show up on most error code reading apps and you have to clip two pins together in obd2 port to read and those error codes via blink codes. I think @ChapmanF above has some links for how to do that. Or just do a google search with these keywords "priuschat read clear blink codes"
Back on March 12,2025 you reported having the red triangle and another warning light in this post, https://priuschat.com/index.php?posts/3522267 You were given the same advice about needing a more capable scan tool to read the trouble codes. Did you ever fix the problem that you were having back in March? Is this new thread just a contribution of the problem that you first reported in March?
It's right on the PriusChat wiki: Blink (a/k/a Flash) Codes – How to. | PriusChat You can get brake system codes that way (and several other systems). But, generally, codes that light the red triangle, you can't. You need a capable scan tool.
