scanmaster is very important. tells you whats going on w ure car. its a dianostic tool that will aid in ure cars health. first thing i should have done. instaead replacing headgaskets was the first thing!if i had the scanmaster i would have saw i was having knock issues and would have been able to address them. next thing would be chip at the very least if money is tight and if not do chip and injector. but scan master is numero uno!!! i sold my gn and looking for a new one. i already purchased a scan master