This Oxygen (O2) Sensor light in a Daihatsu Feroza / Daihatsu Rocky / Daihatsu Sportrak will automatically come on around 80,000 mi (128,747.52 km), at which time you should replace the sensor.  The replacement is a stock Daihatsu Oxygen Sensor or a Bosch Oxygen Sensor (#BSA11027).  After replacing the sensor, the light will remain on until you REMOVE THE BULB (Combination Meter Removal Instructions), that is what the Daihatsu Service Manual actually says.