Cars

When you take your (modern) car for a service,  multiple sensors provide information about the service shop on how things are going. Generally, the service staff figure out through their own experience what might be needed based on what the sensors are showing.
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The body

Similarly, we are seeing more health metrics being available with FitBit-like devices. There have already been cases of a FitBit indicating pregnancy. Diabetes sufferers can now connect constant glucose monitoring systems to their body.
How machine learning will change this
Based on the sensor information and past cases, machine learning will train itself to flag when something is wrong. The person (or car) will go to the doctor (or service shop) to have more thorough testing done.