Steve
I had a Lambda failure on my 125 last which I diagnosed by the loan of Nick's lead (so useful I have since bought my own). I just installed Easimap on my PC, connected the USB, the lead to the connector to the right of the steering column under the scuttle, turned on the ignition and it connected.
The symptom I had was that once warm the car wouldn't run cleanly at a constant throttle setting / speed.
Easimap showed that the Lambda output was a constant voltage and not going from I think 0.8 to 1.03v constantly once up to temperature.