Hello,

I'm currently in the process of going through a newly acquired 300CE of mine and the O2 sensor was among one of the first things I wanted to replace before sending the car off to get smogged.

I replaced the O2 sensor with the Ford part and spliced the wires onto the original harness. I was testing the connections when I found that the black signal wire is giving me a constant 800 mV reading even when the car is fully warmed up. The white heater wires were giving me the correct 13.4V, battery level. I tested the voltages in parallel with harness from the O2 still connected under the floor mat. I used the metal screw in the footwell for ground against the black O2 signal wire.

My question is, what should I be looking at now that I've discovered that the signal is not fluctuating? Is this a sign of a bad fuel mixture setting? Adjustments at the EHA/Lamba Tower?