I can't give you exact details of parameters upon the entry into limp home mode, but I can describe it generally.

Once the system senses extreme error in the input from particular sensors, it determines that there is a serious problem and ceases to manage the engine normally. To prevent your being totally stranded, it enters limp home mode, which allows the engine to run, but at a very degraded level of performance.

The idea is to allow you to get home rather than walk to a phone booth.

Have a great day,