The Mercedes Benz ML320 uses four oxygen sensors in the exhaust system. Before replacing all of them, have the dealer or other service center scan the computer for codes that will indicate which sensor is failing. The sensors lock into the exhaust system just before and after the catalytic converters under the car. Replacement sensors are available at most auto parts stores and through your Mercedes dealer. Bosch manufactures the OEM sensors as well as replacement sensors for the Mercedes ML320.
Raise the front of your ML320 with a jack then position a set of jack stands under the frame to support the car. Lower the jack until the car is resting securely on the jack stands. Remove the jack from under the car.
Position yourself under the car just behind the front wheels. Locate the catalytic converters in the exhaust system then select the sensor you need to change. There are two in front of the converters and two behind them.
Follow the wiring harness coming out of the top of the O2 sensor to the connector where the sensor wires and the car's wiring harness join. Release the locking tab and separate the connectors.
Place an O2 sensor socket over the sensor then turn it counterclockwise with a ratchet, removing the sensor from the exhaust pipe. Discard the old sensor and install a new sensor in the threaded hole on the exhaust, tightening it with the O2 sensor socket and ratchet.
Plug the wiring harness connector from the O2 sensor into the connector on the car's wiring harness, making sure the locking tab engages the connector. Repeat these steps on any of the other O2 sensors that require replacement.
Raise the front of the car off the jack stands with the jack then remove the jack stands from under the car. Lower the jack and set the car on the ground.
