I've been doing some reading about this, and interestingly the original notice of violation issued by the US Environmental Protection Agency doesn't mention crash sensors. The letter is here:
[click]. It alleges that the defeat device "senses whether the vehicle is being tested or not based on various inputs including the position of the steering wheel, vehicle speed, the duration of the engine's, operation, and barometric pressure". Surely, if it uses the crash sensors to detect that it's being tested, then it doesn't need to do all that fancy stuff involving the position of the steering wheel and the speed?
What's also interesting is that, even if the VW defeat device were operable on the roads (assuming the driver drove at the correct speed, etc), it would still be illegal. Credit here to the lawyers who drafted the regulations, because they did an excellent piece of work. The relevant regulations are here:
[click]. VW are accused of a breach of §7522(a)(3)(B) because the software was designed to beat the tests whether or not it was also operable "on the road"; and a breach of §7522(a)(1) because they had not declared the device and obtained a certificate of conformity for it.