Lambda management is quite complex.
The error may be reported to various causes. Reports whether the signal comes out of a lot of parameters (and you can read values very often near to +/-20% which is the limit), or if the value is not provided by the ecu. If you try to send a fixed value of volts at the entrance of the ecu, simulating a lambda 1 value (and you read about the DTM the value 0), the ecu notice of this because it does not detect the correct value at various stages of the engine, and will give you error ...