When and why does embedded Electronic Control Unit(ECU) use default calibration values?

Typical embedded ECU stores real calibration values and default calibration values in Non-Volatile Memory(NVM).

Let's say ECU is Steering Controller and it's primary function is Lane Keep Assist(LKA). It is mounted in a commercial truck. It programs camera's real and default calibration values in NVM.

Mostly, real calibration values are used. When and why are default calibration values used?

Fairly obviously, when it's first powered up - as is clear from 'default'. If something happens that trashes the current settings, I'd like to assume that the defaults are restored to regain operation.

I'm guessing there is some kind of learning algorithm that gradually improves the system. If the "latest" values are lost then start again with the default (start) values.

Mike.

In the case of an engine ECU, you need default values in case a sensor is bad. An oxygen sensor needs time to warm up, so it needs a value to keep the car running. The car runs in a "open loop" condition typically a certain engine temperature is reached.

Some information can be gotten from the "drive cycle". https://epa.ohio.gov/Portals/27/echeck/docs/OBDReadinessDriveCycles.pdf
This is part of the tuning process.

A crank position sensor failure, you can't not have. You can approximate a MAF, a Mass Air Flow sensor. I had a case where the sensor was bad, but the car would not continue running. It did, when the connector was pulled.

i had a 2019 with LKA, atuo pilot works great until there was oncomeing traffic, then it would drift in to the other lane and disengage to manual control, I also enjoyed how it would lock up the breaks and jerk me around if i didn't squeeze the steering wheel tight enough.