STAR is the diagnostic software that MB and decent Indies use to assist in diagnosing faults it checks all systems on the car, a quick test does an overall test of all monitored control units throughout the car, it is far more comprehensive than any other diagnostic system, if the ignition is turned whilst the airbag is disconnected it will register a fault in the cars computer, this light will stay illuminated until its reset by STAR, If any of the units are disconnected and the ignition turned on it will log a fault in the computer. I normally have quick test done on my car once or twice a year just for peace of mind really, last time it told me that i had removed replaced my interior light cluster and A/C control unit though these logged faults won,t stop the car from being used, when you do get a fault and the codes are read there will be superflous codes stored that could confuse the diagnosis, and as i,m always playing about with mine i like to know that all codes are cleared every so often.