Most Lambda Sensors can be carefully cleaned which saves replacement at huge cost. It often happens as the result of cheap or contaminated petrol and thereby 'throws' up DTC's indicating Lambda sensor failure. Some 'fuel additives' might improve ignition but there are some which cause Lanbda sensor problems and DTC's. Before replacing try cleaning them, nothing to lose.

 

How does cleaning work? Rinsing them in some specialized fluid ?

What is the effect of green, orange,... coolant chemicals to the sensors (from head gasket leaks) ?