Oxygen, Lambda Sensor Exhaust Oxygen Sensor (O2 Sensor) Measures oxygen in the exhaust so the ECU can correct the air-fuel mixture EFI "301809" - Not availableAUDI - Q7, A4, A6, S6, A3; BMW - 3, 5; CITROËN - Xsara, C5; FIAT - Doblo, Panda