Oxygen, Lambda Sensor Exhaust Oxygen Sensor (O2 Sensor) Measures oxygen in the exhaust so the ECU can correct the air-fuel mixture RIDEX "3922L0491" - Not availableBMW - 5 (E39, WB), 6, 3, 7, X5; PEUGEOT - 306, 206; CITROËN - Xsara, C5