Does the 'Check Engine' light come on when there are trouble codes generated or is it possible minor trouble codes can be generated that will not necessarily activate the 'Check Engine' light? Thanks.

 

good question.

check engine light got direct monitoring on O2 sensors and knock sensors. it also check the resistance value of the components and anything between that, it will store the fault on concerned party.

it can also store soft codes which deduct itself as you start and stop the car whenever that fault is no longer detected.