Nissan Repair: 240sx o2 sensor, air fuel ratio, o2 sensor

Question
hi, i bought a air fuel ratio guage that i would liek to hook up to my 240 and in the instructions i have to find the signal wire fromt he o2 sensor that connects to the harness, and i do not have a manual to my car, i do not want to cut the wrong wire and have to replace a 70$ o2 sensor because of a $20 guage

Answer
Gerard,

If you have a one wire oxygen sensor there is only one wire to cut.  But, be sure to solder the wires as the oxygen sensor is a self generating device and any excessive resistance in the circuit will give the computer bad data.  If you have a three wire sensor the other two wires are for heating the sensor to get it up to operating temperature quicker.  This way the computer can get the emissions under control faster.  To check which of the three wires is the one sensing information you basically unplug the connector and, with a test light, back probe the connector that goes to the car and fine the power and ground.  The other wire is the one that receives data from the oxygen sensor.  Not that you wanted to know all of this since I am sure that yours is a one wire oxygen sensor.