[pmax]

http://forums.pelicanparts.com/porsche-911-technical-forum/874460-help-lambda-freq-valve-test-please.html

http://forums.pelicanparts.com/porsche-911-technical-forum/821090-cis-lambda-frequency-valve-signal.html

It shows what the "ECU" is sending to the FV. Put a scope on the correct 2 wires and it shows the signal sent to the FV.