TL;DR: When I start the car, it turns on but the drivetrain clearly isn't on. A/C doesn't start and it neither the motor nor the engine are running. If I shift out of park, it says "Action needed - Shift to park" and of course won't drive. The check engine light is also now on.

It's a 2017 Volt Premier with 111km miles on it. Should I replace the battery first, or take it straight to the dealer? They want $220 just to diagnose it, so I'm wondering if it's worth $250 on a battery just to try. Has anybody else had this issue?

If it is the BECM, is there any reason that it wouldn't be covered under warranty? The dealer looked for about 30 seconds and didn't see anything for N232432680, but as soon as I said anything about it, he just said he'd have to get it diagnosed first.

The details:

It started when I bought the car in March. I drove it around at first, and it was fine. Then suddenly it did exactly this. I should have backed out right there. But I got it charged up and managed to get home. I knew similar things could happen from the batteries all being depleted for an extended period of time, which was definitely the case. But on my way home that day, it died several times and I ultimately got it towed home. It would go to battery power only, but it would only get me far enough to pull over. I got it most of the way home by shifting back to mountain mode and charging up, until it all just died one time and I couldn't even jump it. I did get the battery tested that day, and it was fine, but I got the dealer to give me $500 off the price in case it needs a new one.

When I got it home, I charged it overnight, and I haven't had a single issue since (6 months) until today. I just went to start, and boom, same thing. I charge it at home, and it's clearly charged.

Why it might be the battery: It doesn't have the typical BECM signs. Mainly, it shows me that the main battery is full and the mileage on it.

It isn't the usual "shift to park" issue: I have no problem with it not believing that it's in park.

Why it might be the BECM: It's a battery issue of some sort, clearly. Even if it isn't the typical symptoms, there's always a chance. And being at 111k, it may be worth it to try and get it replaced before it's too late.

I'm planning on my next car being a PHEV. People over on r/PHEV have mentioned first gen Volts are fairly reliable and maybe (?) more so than second gens. As these are older cars, finding a low mileage vehicle isn't easy, so I'm curious about cars in the ~100k range. I have read about issues with both the engine and battery coolant levels running low and causing problems. A listing I am looking at is a couple of hours away on a first gen Volt. It mentioned replacing the "coolant level sensor" in the ad. Is this potentially a warning sign of deeper issues with one of those systems? In general, what should I be on the lookout for on a 2013-2015 in the 100-125k range.

FWIW, I'm coming from an 09 Honda Fit that I love, but it is at 200k miles. I'm looking to hopefully transition to a more efficient vehicle that has good reliability (though I don't know if anything could beat how reliable my Fit has been overall).

My 2015 cold died ( probably ICE engine sized, don't have complete diagnostic yet) . The car was not in good shape to start with so it does not worth the repairs.

So I brought a 2014 Chevrolet Volt cuz I'm truly in love with this model .

I want to keep the old one for parts but the battery was empty when it died so I suppose it would be better to charge the battery before storing it. The problem is, the OBD2 is full of error message, a can clear them but they come back as soon as I power the car prevent it to charge.

Is there a way I could make a one time bypass of that just to charge the battery once ? I don't want to drive the car or anything, I just don't want the battery to die under my watch.