Check eng lite, 2017 Prius Prime

I've read that when 12v battery dies, all sorts of error message lights up on the dash. If you successfully resurrected the 12v battery and the car is starting and driving normal, chances are the error is nothing to worry about. But without code reader, it is impossible to say what error code is in the memory. Maybe stop at any auto shop just to have it read the code? If nothing to worry about, then you can ask them to erase the code.

 

I'm guessing that your 12V battery is not holding its charge even after one overnight charge session. It may require multiple sessions to get it back or it may be toast due to the deep discharge of 10 weeks inactivity. 12V batteries don't handle deep discharge well at all.

I'd get it to an auto-parts store or some location that can do a real battery test. Don't put this off. You're on very short borrowed time. If your CTEK can do a test, try that first. It may still not hold a charge.

When my battery died in my 2010 Prius, it gave me all sorts of strange dash lights and errors, but it did not throw any codes. It was running in the 11 volt range and was not able to power up all the ECU's for the car to act properly.

This is happening to vehicles all over due to non use.

 

it will probably go away on its own after a few drives

 

You might want to be aware that the "Check Engine" light warns of emission control faults, not anything to do with the operation of the engine at all. It is named the "Check Engine" light to scare you into thinking something bad is wrong with the "engine" so that you will take it immediately to the dealer for repair. Apart from the low 12V battery, other common reasons the "Check Engine" light will come on is a loose gas cap (fuel vapor containment) and catalytic converter faults--there are O2 (oxygen) sensors placed in front and behind the catalytic converter and they measure the amount of oxygen going into and coming out of the catalytic converter. If they are the same, the catalytic converter is not doing its job--it is supposed to eliminate excess oxygen in the exhaust gas, lowering harmful emissions.

 

Check engine light can be triggered by a temporary anomaly, say a connector pushed back together but took a split second too long connecting with the CPU. The fault may be resolved, but the light will persist for 4~5 start ups.

I had a check engine light after one Intake Manifold and EGR clean out, various connectors were disconnected/reconnected. First start up after, argh: check engine light. About a day later, after a few start ups, it went away.

Have a dealership (for a cost) or automotive retailer (usually free) check the battery's condition with an electronic load tester. Or you can DIY with something like Solar BA9. For starters, just check it's voltage, first thing in the morning, car off, with a multi meter.

 

In general, if check engine light goes on, it takes 3 start/stop cycles of the car for it to go off if the error has not persisted in my experience.