My 2015 Prius had been sitting for several months without being started. The starter battery went flat so when I turned it on, the dash turned on and off in a loop.

I charged the starter battery to full, and tried again. “Hybrid system error, see dealer”. The hybrid system indeed doesn’t run, only the ICE engine runs when I drive it.

There are many ODB-II codes, which I have exported to a file. But the only pending, confirmed, failing test is: P602F(46) ECM “eeprom error”.

I am wondering if it is okay to clear all these codes, since I imagine the low starter battery voltage (and multiple cycles) really confused the electronics.

Could clearing possibly fix the issue, or is that wishful thinking? Should I clear, or take it to the dealer as is?


After I had recharged the starter battery, I exported the codes to a file in case I needed them later. Then I cleared all the codes and restarted the car. Great news, the hybrid system is working perfectly again, and no codes have returned. (I'll update this question again if I regret this down the line!)

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    Welcome to Motor Vehicle Maintenance & Repair! Commented Sep 17, 2023 at 21:24

1 Answer 1


The first thing I do when checking any vehicle is to clear the codes, that way I can see what comes back up afterwards. Those are the codes you look to see what issues the car might have. So "should you"? IMHO, yes.

Most likely, clearing the codes won't fix your issues. All it's going to do is point more directly to what actually the problem might be. Especially since it's saying there's an EEPROM error. That sounds like there's an issue with computer which runs the hybrid system.

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    Thanks, this helps. I just wanted to make sure I wasn’t going to make things harder for the dealership if I do need to eventually take it in. Sounds like real issues will continue to be reported as code though. Thanks
    – aaaidan
    Commented Sep 17, 2023 at 21:31
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    I think that clearing the codes would be a bad idea if you plan on taking it to the dealer. They may be able to utilize the information to come to a more accurate diagnosis. Now if you were going to try and diagnose this yourself, you could record the codes and types and clear them as Paulster2 said.
    – Jupiter
    Commented Sep 17, 2023 at 23:19
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    @Pᴀᴜʟsᴛᴇʀ2 My understanding is that some codes will occur only during certain conditions. Thus, if you clear codes that only occur during those conditions, and then take the vehicle to a mechanic, they will have no idea that such conditions occurred. This will make it much harder for them to diagnose issues that only occur in specific conditions. Commented Sep 18, 2023 at 6:44
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    @RockPaperLz-MaskitorCasket As a software engineer who's previously worked on ECMs, I can confirm that this is correct. Also faults caused by loose wiring /connections may genuinely go away temporarily if the connection is made temporarily, and this will happen when the car is stationary and you're looking at it; but they'll tend to come back when the car starts moving and knocks the connection.
    – Graham
    Commented Sep 18, 2023 at 7:15
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    Yes, when doing a diagnosis, clearing can be very beneficial. But if you are leaving the vehicle to be diagnosed by someone else, the information that was cleared would have been crucial in a good mechanics tool belt for a better and quicker diagnosis. Most mechanics upon hearing that the customer had cleared the codes are thinking and many times saying to the customer that they shouldn't clear them.
    – Jupiter
    Commented Sep 18, 2023 at 10:57

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