Does 17931 dtc prevent the car form start or in detail the coils from firing?
Nope. Starts and runs just fine with this dtc present.
Have you done any logging or viewed any measuring blocks to see if its really not having any affect on other functions throughout your EMS?
I would imagine with our cars having a relatively solid reputation for crash test safety, that a DTC like this being present in the system, you would assume some technician would have put in place some type of restrictions, capping engine performance at a certain point due to the ECU reading that there is no airbag present and therefore it would be unsafe to reach high power output levels with a properly functioning air bag module lacking of presence in the vehicle help protect you or your passengers in the event of a collusion or accident of some sort.
... In my opinion I think that would be reckless for an automobile manufacturer to not put a maximum power output cap in place in the event of an airbag malfunction or if an airbag had been deployed... If you were driving 70 - 85 mph on the highway and hypothetically, say you got in a huge crash and the operator of the vehicle along with its passengers were all injured or killed as a result of the accident, there could be substantial lawsuits against the manufacturer for the reason that the automobile manufacturer didn't do enough to prevent a tragic and life threatening event such as this from occurring.
Regardless, you could be correct. There might be no differences in performance, but I can't personally see an automobile manufacturer letting that happen?