I want to upgrade my car (TPI with TES headers)to a heated o2 sensor. I just bought one (NGK unit) from www.goautocenter.com but it has 4 wires. I understand the wiring for a 3-wire unit but cant figure the coloring for this one, and what I should do with the fourth wire.

The colors are as followed.
white, white, black, grey

Thanks

 

Two white wires = switched 12v (+ and -)

Black wire = sensor signal output

Grey wire = sensor signal ground (hook up to a good ground)

A four wire sensor not only heats the sensor but it also has a dedicated ground wire for the signal. It does not ground through the exhaust manifold or header like a single or three wire sensor.

[This message has been edited by TunedPort350 (edited May 13, 2001).]

 

Thanks for the quick reply, but that being the case, couldn't I just get a good common ground and wire one of the white wires to the grey wire?

 

No, you would not want to do that. Tho O2 sensor output is in the millivolt range, and you would not want to ground it to a wire carrying any current, which would cause a varying, noisy, voltage drop across the wire. The O2 sensor ground to the ECM is generally connected to the back of one of the cylinder heads in one wire O2 sensor systems - connect it there. I'm surprised that NGK didn't use the black wire for the sensor ground........

Tim