Lambda (Oxygen) Sensor. One supplied, but this item suits both Pre-Cat and Post-Cat positions.
This item is located in the exhaust system before and after the catalytic converter. (Early Mk1 172 models only have 1 sensor) These measure oxygen content in the fuel mixture to regulate the fuelling. A faulty sensor can lead to hesitation , poor performance and fuel consumption.
Genuine Renault or OEM Manufacturer Bosch units available.