Mercury BE5Z-9G444-A Lower Oxygen Sensor

To service an oxygen sensor, warm the engine before removal to prevent damage. Avoid harming the pigtail or electrical connector and keep contaminants away from the sensor. Do not use cleaning solvents. Handle the sensor carefully and ensure the silicone boot is correctly installed. To replace the upstream sensor, locate it, disconnect the connector, and unscrew the sensor with a wrench or sensor socket. Apply anti-seize compound to the threads if reusing. Repeat the process for the downstream sensor.