Symptoms point to a leaking head gasket. An expensive repair unless you do it yourself. There could be other internal damage to the engine as a consequence of coolant loss and overheating.
The white vapor suggests some coolant steam is being expelled to the outside of the gasket. The hissing indicates engine compression getting into the cooling system’s plumbing - another indication of a head leak.
Can you get a readout of what is causing the EML (AKA CEL, Check Engine Light, or MIL, Malfunction Indicator Light)? This does not always come on in case of a head gasket leak, but may give a clue as to what’s going on.
needs to be addressed. if the system does not hold pressure the engine will overheat, and you will lose coolant. I am not familiar with your specific car, but you can be losing coolant through the overflow tube if it has one.