My 2007 Prius recently started having this happen...when I would start it normally, the dashboard will light up with practically every light. I have an OBD reader and hook it up and it shows 99% of the time no code. Then I erase the "no codes" and the lights disappear and it drives fine. That is until I turn it off, when I start it again , it does the same thing. I have recently left the OBD ready plugged because if I erase the codes it drives fine. But I know it isn't fine or it wouldn't be doing this! It began months ago after heavy rains. I began to think it had something to do with water, since I drive it for delivery and had driven through plenty of water. It did it for several days, then stopped and was fine for months, then it would begin again after rainy weather. It has not been driven in water lately so I don't know what to think about it now! Plus is will not stop doing this, it has been about 2 weeks in a row that it does it every day. Oil is changed regularly. The few times it does actually show a code is PO301. Any suggestions? Thank you!
The type of phone app and OBD2 device you're using is likely the cause of a lack of information on dash lights. Also please tell us what region in the world you live in to give us a sense of the kind of water you're talking about? Without more information it's hard to be certain. But if I had to guess I say it could be moisture in the spark plug hole where ignition coil plugs into spark plug. So I'd remove those and make sure everything is dry and switch the position of the ignition coils to see if P0301 changes to a different cylinder. But that's just the start because P0301 is just the check engine light, not all the dash lights. And again back to your phone app, you need an app with hybrid car library of error codes, which might explain it. If you know someone with a different code reader, try that as well.
P0301 is an engine code, and you're not seeing any codes responsible for the ABS and VSC lights, so you've got an OBD reader that is able to talk to the engine but not to the brakes. A lot of people run into that. When you have brake warning lights and you don't have a reader that can show you those codes, do this: Blink (a/k/a Flash) Codes – How to. | PriusChat
I have a OBD reader that I plug into the spot under the steering wheel that has a connected remote that has options to read , then erase codes. I also have the Dr. Prius App on my phone with the OBD control. I have only used the manual one so far. I live in the Midwest, it has been very rainy here this summer!!
We have a whole thread here put together with extensive effort by mr_guy_mann about which OBD readers you can get for a Prius and which ones will and won't be able to show you all the codes you have: Gen2 OBD2 app review | PriusChat