1. When the ignition is switched ON (engine off or on), the instrument cluster receives (1) an check fuel cap warning light illumination request signal from the PCM via CAN communication.
2. The instrument cluster turns the transistor on (2) based on the check fuel cap warning light illumination request signal.
3. When the transistor turns on, a ground circuit with the check fuel cap warning light is established and the check fuel cap warning light turns on (3).