Wiring question - O2 sensor pin in ECU wiring harness
 

I've looked in the Haynes manual, and not having too much luck with finding a way to identify wires in the wiring harness. Can anyone identify which of the wires on which harness goes to the O2 sensor?

I would have tried tracking the wire by color, but it seems my O2 sensor wire has been repaired along the way, albeit poorly, and I can't seem to find the original wire.

Collin

In the wiring diagram chapter of the online FSM, it shows the O2 sensor circuit to be color coded GY (green with yellow stripe). It shows up on pin 2D at the ECU connector, which should be 2nd from the (right?) end, bottom row, of the middle-sized (18 pin) connector. Triple check that the color code agrees with the position of the pin before you cut anything. This is all for an S4...

See pg. 50-117 for the color codes, and 4a-30 for the functionality. See also the pin assigments for the 3 ECU connectors on pg. 4a-32.

NOT green/yellow but GREY. It's a grey shielded cable with a black center conductor.

GOTCHA!!!!! humor

My o2 sensor wire on my S5 vert is Black.

The wire connected to the ECU is black, but if you follow that black wire back into the harness, you'll find it is the center conductor of a Grey shielded cable. Or if you follow the black wire from the 02 sensor back into the harness you'll find it is the center conductor of a grey shielded cable. Shielded because the output of the 02 sensor is in millivolts and can be influenced by EMI if not shielded.

Mine is not shielded. Is that an S5 thing?

Grey?

My 86 manual says color code "G" = green, and "Y" = yellow.

It shows the color code of the wire going from the O2 sensor to the ECU as "GY".

The online 86-88 manual does not have a listing of the color codes, but also lists that wire as "GY"

Mine is unshielded (though it might be nice if it were shielded), green with a yellow stripe. His car is an S4; is there some reason it might be different than my S4, and different than the manual?

The 86 and 87 FSM's that I have show the color code of the wiring. BUT it does not show GREY.

That said, in the 86-87 FSM's, the wire is shown as Gy. Notice the lower case *y*.

Now I've fooled around with the three clunker RX I own, and messed more than once with the 02 sensor connection at the ECU at pin 2D. I KNOW it's a black center conductor and if that black wire is followed up the harness, one fins it come out of the grey shielded cable and the shield of that cable is grounded right there.

IN other words there is no true explanation of why MAZDA did not include the GREY wire in their color codes.

See NZCONVERTIBLE's posts where he tries to explain it.

In the engine bay, that grey cable is most likely to be more burnt brown than grey ....until you undo the harness wrapping further in the harness. Then it's plain grey shielded wiring with a black center conductor.

I also meant to mention the SHIELD SYMBOL is shown on the wiring diagrams where the 02 sensor and the knock sensor are shown.

The thrid gen dwg shows Gy for grey and G/Y for green/yellow. It also gives an example of what the shield symbol is. See third gen attachment.

Thanks guys this one helped me hook up my A/F gauge. The wire on my S4 vert was black at the ECU on the 2D 18 pin connector as stated in a earlier post by Calpatriot and Hailers. Thanks guys for the knowledge, I will be asking about random connectors in my engine bay thats just hanging around not plugged to anything...