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Green Light
A green light indicates that all engine systems are running normally, which means that all emission monitors are active and performing their diagnostic testing, and no DTCs are present. The vehicle is ready for a Smog Check.
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Yellow Light
A yellow light indicates that there is a possible problem in one or more of the vehicle’s systems that may prevent the vehicle from passing a Smog Check. Either a Pending DTC is present, and/or some of the vehicle's emission monitors have not run their diagnostic testing.
Red Light
A red light indicates a problem in one or more of the vehicle’s systems that will prevent the vehicle from passing a Smog Check. The red LED is also used to show that DTC(s) are present as shown on the scanner's display screen. In this case, the check engine light will light be on in the vehicle.
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