Hi Guys
I'm replacing my rear O2 sensor with a Bosch OE (2004 Manual). However it was previously replaced and the OE connected was cut off. Does anyone know what color the sensor wire is coming from the onboard computer to the O2 sensor? And also the color of the 2 heater wires? And just curious why does the rear O2 sensor have a heater if its in the Cat? I understand the front one having a heater but why the rear? I've looked all over and can't find a wiring and color diagram.

 

This will show you the wire colors for the O2 sensor:


And here is the color code chart:


To work efficently, the sensor must be heated (600+ degrees) and built-in heaters will heat the sensor up quickier than the engine will (factors such as ambient temps could prolong it).

 

Thanks Jon. Your like a magician or something. I never knew they got so hot on there own, but it makes sense now. I have another question. I looked at the diagram and I could only figure out the ground wire from the obvious symbol. But I'm still unsure which 2 wires are the heater wires and which is the sensor wire. I see 2 wires going to the pcm which i'm guessing one of those must be the sensor wire. But really I'm just guessing.

 

Might have been easier to tell if you saw the full page, but the W/R wire coming out of the O2 sensor goes to the Main (EGI) relay and its what energizes the heater.
So it'll be:
Y = O2 Sensor Signal
BR = O2 Sensor Ground (to PCM)
W/R = Heater Element 12V
R = Heater Element Ground (to PCM)

 

Jon can you please help me, you see I have to change my rear o2 sensor, and because of my budget I had to buy a generic one. Now I have a big problem, I need to wire up my new o2 sensor to the connector of the old sensor, and the colours don't match 😭😭😭😭 in the old sensor the colours are one blue, one white and 2 black. And in the new sensor there is 2 white, one black and one grey. I have a Mazda rx8 2006 btw lol. Please Help!!!