No. But it is so important we strongly recommend you have one.
An O2 sensor is mounted somewhere in the exhaust system and measures the amount of Oxygen present in the exhaust gasses, from this information the ECU can determine whether there is an excess amount of fuel present (called rich) or a lack of fuel (lean).
All Link ECUs can monitor and protect against fuel conditions too rich or too lean which could lead to damage to your engine. But not only this, all Link G4X ECUs are able to actively adjust the fuel mixture not only to protect the engine, but optimise the fuel delivery for the most power!
We recommend our Link CAN Lambda https://dealers.linkecu.com/can-lambda it connects to any G4+ or G4X Link ECU and provides reliable accurate wideband O2 readings.