What does the red LED indicator mean on the Code Reader?

A red LED indicates there is a problem with one or more of the vehicle's systems, and that Diagnostic Trouble Codes (DTCs) are present in the vehicle's computer memory. In this condition, the Malfunction Indicator Lamp (Check Engine light) on the vehicle's dashboard will be lit steady. A vehicle displaying a red LED is not ready for an Emissions Test (Smog Check) and should be inspected or repaired before driving further. (Page 19)