Modern cars are rolling computers with dozens of interconnected ECUs that...

https://iris-wiki.win/index.php/Why_Does_My_Check_Engine_Light_Keep_Coming_Back%3F_Stop_Clearing_Codes_and_Start_Fixing_Cars

Modern cars are rolling computers with dozens of interconnected ECUs that constantly talk to each other. When a dash light pops up, a basic OBD reader only gives you a surface-level code