O2 Sensor Identification GuideAn OBD Scan Tool will usually identify Oxygen Sensors by the Bank Number (B1 = Bank 1) and Sensor Number (S1 = Sensor 1). Bank 1 will always contain Cylinder 1, which is located closest to the front of the engine. Part manufacturers often use different terms than scan tools to identify sensor positions. Regardless of the vehicle's engine orientation, the right or left bank is determined by viewing the engine from the rear (opposite the drive belts). A Upstream Sensor (Before Converter) B Downstream Sensor (After Converter) C Left or Front Upstream Sensor (Before Converter) D Right or Rear Upstream Sensor (Before Converter) ![]() ![]() ![]() ![]() Common O2 Sensor ContaminantsOxygen (O2) Sensors commonly fail due to contamination. When checking or replacing an O2 Sensor, visually inspect the sensor body to determine if it has been contaminated by a faulty part or substance upstream, and correct the fault before replacing the sensor.
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