These are just some of the warning lights that may come up on your instrument panel.
They should come on when the ignition is switched on and then go out when the engine is started.
If they come on while driving, either flashing or permanently on, they will have logged a fault
code in the relevant ECU (Electronic Control Unit) because a fault has occurred.
There may or may not be any drivability issue but the warning light has come on for a reason.
If on the next journey the light does not come on the fault code will still remain logged in the memory
of the ECU.
To find out the cause we connect a diagnostic scan tool to the vehicle and interrogate
the relevant system, scan for any fault codes and view the live data to see if any parameters 
are incorrect. The live data and fault codes present will help us to look at components or conditions
that could have triggered the fault code.
These then have to be investigated and components tested to confirm the fault.
Only then can corrective action be taken, either by replacing a component, sensor or remedial
work carried out. Because some faults can turn out to be complex and difficult to locate, the customer will be advised (in all cases) of
relevant costs and parts required as the work proceeds so as to ensure that they are well informed.
The myth that people say "get it code read and it will tell you exactly what's wrong" is not usually the case. Fault codes will
often have descriptions that contain the following -  implausible signal - out of range -
signal too high - signal too low - open or short to live or ground - electrical malfunction - limit exceeded -
intermittent fault ,....and so on.
The code description will not say "replace coolant temperature sensor, it's faulty"
 if only it was that easy !