Thank you for your fast reply.

The sensor has, 2 white wires, a grey wire and a black wire. I take it the grey and the black are a trigger and an earth, I dont know what is what or how to test the trigger.

And why am I getting just 4 volts out of one of the feeds to the white wire?

Update} just found this http://www.lambdasensor.com/main/mcolours1.htm says the black is the signal.

Got a meter no sure what or how to test,? thanks all.