An Oxygen (O2) Sensor helps calculate/monitor the air & fuel mixture for combustion. Most modern vehicles have more than just one O2 sensor, and should be replaced all together. A faulty O2 sensor can easily cause a check engine light (trouble code), rough/erratic engine idle, poor fuel economy, and even engine start up issues. Mando O2 sensors are OE replacements with factory precision specs. Choose Mando O2 Sensors to re-maximize your Hyundai or Kia’s original engine efficiency and performance – We Are OE!