I've noticed this a couple times and I cant figure out why. I have a suspicion that it allows a maintenance tech to check the transmission fluid. My understanding is that checking it is much like most manuals, remove the upper plug and reach in and if you can touch fluid, its fine, except in the Volts case, the ICE must be running.
Why does the engine start when the hood is opened and car is "on"?
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You are correct, the ICE will run whenever the Volt is powered on and the hood is opened so that a Volt technician can perform certain vehicle diagnostic procedures.
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Imagine that the engine does not start with the hood open with the car on. You wouldn't want to be working under the hood if the engine could start any time.
It is a safety measure too keep you from working under the hood with the car on.
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From the Gen-1 (2015) Manual, p. 9-21: "In either Electric Mode or Extended Range Mode, when the hood is open, the engine will run without turning off if the vehicle is on. The high voltage battery is neither charged nor discharged when this occurs."
In other words, it's a feature that the engineers designed into the car. A couple of reasons come to mind: (1) to facilitate maintenance, e.g., leak tests, etc., and (2) to enable an emissions test.
I'm sure it's a safety feature as well. Imagine not realizing the car is "on" and performing work in the engine bay. It's very easy to forget the car is turned on if there isn't any engine noise. One thing I have noticed is that the engine won't turn on if you open the hood while pre-conditioning. It just turns the pre-conditioning off. Again, probably a safety reason behind that. Not sure if traditional ICE powered cars turn the engine off if the hood is opened without the key in the on position.
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Interesting. Good to know, thanks.
Is it known whether "precondition can use ICE" is set on or off when that happens? I mean, I'm already fully behind the "precondition is not an ignition-on state" and it will not start regardless, but it would be interesting if the other were true and and opening the hood with engine-heat-enabled preconditioning DID start the engine regardless of ambient temp.
I actually realized how the ICE won't start in preconditioning as I was running a cycle as I was leaving work to cool the cabin and a co-worker asked to see the engine. I opened the car and popped the hood and the preconditioning cycle ended. It wasn't a time issue as I had just initiated it less than 2 minutes prior. I did it again and the same result, so I can only assume that is a safety feature for the preconditioning cycle. Also, when the hood is open and you try to initiate a cycle, it won't.
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