Oxygen, Lambda Sensor Exhaust Oxygen Sensor (O2 Sensor) Measures oxygen in the exhaust so the ECU can correct the air-fuel mixture NTK "1723" - Not availableVW - Golf, Jetta, Touran, Tiguan; AUDI - A4, A6, A3, A5, S6, A8, A7, A1, Q7, Q5