Mode 1: Mixture Ratio Feedback Control Monitor "A"

During normal vehicle operation the ECU is always in Mode 1. After warm-up and during closed loop operation, the Green LED inspection light turns on when a lean condition is detected and goes off when a rich condition is detected. During open loop operation, the Green LED light stays either on or off, which ever the light condition was just prior to switching to open loop. During open or closed loop operation, the Red inspection light stays off, with the exception of California models that have a "Check Engine" light that is illuminated on the instrument panel. See CHECK ENGINE LIGHT  and MODES 1 & 2 MIXTURE RATIO MONITORS A & B CHART.