The OBD2 system offers valuable information, including diagnostic trouble codes, when troubleshooting problems. OBD diagnostic software communicates with the car and reads the diagnostic information from the car. … The adapter is attached to a car’s OBD2 port. It acts as a bridge between your computer/mobile and the car. Find out why the check engine light or Malfunction Indicator Light (MIL) is on by reading the diagnostic trouble codes (DTCs). After reading the codes, you can reset the Check Engine Light.