Please check fitment notes & description for accurate information. 1999 Toyota 4Runner 2.7L Oxygen Sensor's Location: How do I know the O2 sensor is good or not? Check engine light on A reduction in fuel economy. Your catalytic converter fails unexpectedly Exhaust emissions reach undesirable levels. How to install the oxygen sensor? Step 1 - Some sensors are equipped with a heat shield that must be removed before the sensor removal, this is performed by removing any mounting bolts. .
