Any Daihatsu produced after 1980 was built with an oxygen sensor.  Your Daihatsu oxygen sensor is the part of your emissions control system responsible for sending data to the engine's computer.  The oxygen sensor keeps your engine running efficiently and helps it to produce as little emissions as possible.  Every vehicle has a particular ratio of air and gas that is considered perfect.  Your vehicle's ratio depends on the amount of hydrogen and carbon found in the fuel.  The oxygen sensor can be found in the exhaust pipe and constantly monitors the air fuel ratio.  If the mixture is too lean (has too much air) or too rich (not enough air) then the oxygen sensor communicates these findings to the engines computer.  The engine's computer then makes the adjustments in fuel needed to obtain that perfect ratio.  A faulty oxygen sensor may not pick up that the mixture is too lean or too rich and that can lead to poor gas mileage, hesitation, poor acceleration, surging, and emissions test failure.