Oxygen, Lambda Sensor Exhaust Oxygen Sensor (O2 Sensor) Measures oxygen in the exhaust so the ECU can correct the air-fuel mixture Delphi "ES21316-12B1" - Not availablePEUGEOT - 308, 508, 5008, 207, 3008; CITROËN - C5, C4; DS - DS 3, DS 4