Brake, Handbrake, ABS VSC lights lit

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Not all OBD2 scanners are hybrid compatible, which device are you using to retrieve the stored OBD2 codes?

 

Maybe a bearing or wheel sensor

 

There seems to be a brake issue with the car, sometimes if the car detects there isn't enough pressure (low brake fluid), it can light up the lights.

Since you have MOT inspection coming up, you might want to try and disconnect the 12v battery negative for a few seconds and reconnect. This reset will usually get rid of minor problems. But if the problem is with the Brake ECU, it will need a proper code reader to reset the codes.

But with all braking problems, it's usually best to have it fully checked out by a professional. Coming online to diagnose brake issues can be dangerous.

 

If you have warning lights displayed on the dash, that is indicative of a problem.

View or download the NA Prius owner's manual, pages 5/6 will describe each "dashboard light" and any recommended next steps.

Unless the dealer or an independent hybrid shop can offer a "free scan" to retrieve the stored codes, the next best option might be to pick up a mini-vci cable and a copy of techstream (same software used by the dealership). If you're on a budget, you could grab an OBD2 adapter and a phone app. Which OS are you using? (you can research adapters and apps in this sub here)

 

1. I think you should charge the 12v battery fully first.
2. Reset the car afterwards by disconnecting the battery to erase all the minor codes.
3. Drive the car for a few minutes so the computers can re-detect any errors on the car.
4. Read with techstream again.

The reason you should charge the 12v fully first, the car will give a lot of strange errors if the 12v is low. And while you are doing the diagnostics, you will run down the 12v even more so it'll only give you more issues.

 

Here is the workup for DTC C1343 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/21avn/cic13416.pdf

Here is the workup for DTC C1554 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/21bvv/cic1552.pdf

Here is the workup for DTC B1421 (ignore this DTC) : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2044g/cib14212.pdf

Here is the workup for DTC B1423 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2044g/cib14232.pdf

 

Perhaps it would be good idea to first just concentrate on C1343 572. As the level of fluid is still fine maybe check the actual brake by taking the rear right (passenger side in LHD) brake drum off? Or pressing the brake pedal hard multiple times and just checking for leaks all along the line.

 

Even if it won't change the minds of any true believers, I would be remiss to stop mentioning that I have never, ever seen any Prius do this. I've seen them start if the battery is strong enough, and not start if the battery is not strong enough. I've seen ECUs log specific error codes that mean the voltage got low (i.e., do exactly what they're programmed to do). I've twice seen the Gen 3 MID simply stay off, and not restart until fully power cycled. But the idea that the ECUs will just make up random stuff because 12.08 V? Totally not a thing, in my experience.

My car was kind of a rolling undervolted-Prius lab for a couple weeks recently, when my ten-year-old battery finally rang down the curtain and joined the choir invisible, and while I had to jump it a bunch of times to start it, it never made up any random stuff.