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ID the 4 wires in O2 sensor

Sorry not Volvo but I know you guys here have great answers. My boy yank the wires off the O2 sensor connector by accident when he change out the catalytic converter and looks like the color code doesn't follow through from O2 unit to the connector to the wire harness.

So from the O2 sensor pigtail I have 4 wires: two blacks, one green and one white. The two blacks has a reading about 10 ohms across it and the green and white is open. I assume blacks is the heater with one 12V and the other at ground - polarity makes on difference, right? So this left the green and white as sensor, right? Green and white polarity makes no difference, right also? How many ohms should be measured once I apply some heat to the sensor? If polarity counts, how could I find out which is what?

Sorry for so many questions and thanks in advance.

Reply to
# Fred #
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I'm sure you're right about the black wires, but the polarity is important on the other two. The output is a DC voltage that varies between about 0.1 and 0.9 volts. My guess is that green is ground (negative) and white is the signal lead (positive). Maybe the green wire reads low resistance to the exhaust, or maybe the white one does?

Mike

Reply to
Michael Pardee

Blacks - ground. Green - Heater +12v. White - Signal +0.1-+0.9v approx.

Tim.

Reply to
Tim..

For the connector to the car I found the 12V and one ground but how to verify which terminal is the +signal?

Also resistance lowers across the green and white terminals as heat is applied to the sensor, so shouldn't green be signal ground? Forgot to measure output voltage to verify polarity on the sensor.

Reply to
# Fred #

According to the instructions for a Bosch universal replacement sensor I have handy, there are 4 possible OEM wiring colour combos (that this universal sensor was designed to replace), your combo is "Type C"

signal wire = green heater wires = black signal ground = white

Reply to
Mike F

Thanks Mike.

Is there a way to verify on the car connector which is signal +? If no method is available, I'll reverse the terminals when poor mileage is observed.

Reply to
# Fred #

With the ignition on, the signal wire should have about +0.45 volts DC on it from the ECU.

Mike

Reply to
Michael Pardee

Thanks. Car is running fine for a week, lucky guess.

Reply to
# Fred #

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