Oxygen, Lambda Sensor Exhaust Oxygen Sensor (O2 Sensor) Measures oxygen in the exhaust so the ECU can correct the air-fuel mixture LEMARK "LLB556" - Not availableBMW - 3, 5 (E39, WB), 6, 7 (E65, E66, E67), X5; AUDI - A4, A3; ALFA ROMEO - 159, 156