I bought an after market O2 sensor and I am LOST as to how to wire the plug, (It came without a plug). It has 3 wires..... 2 black and a blue. The original sensor that I removed has a red, white and a black wire. Any ideas which wire goes to what?

 

91 Legacy Lsi 2.2 FWD

 

Thanks a million!

 

Todd

The following is likely, but not guaranteed. The original colors are from Subaru info (although the ''red'' might be ''yellow/red''). The universal replacement colors are from http://www.lambdasensor.com/main/mcolours1.htm

 

Circuit--Original--Universal

Signal---Black----Blue

Heater--Red------Black

Heater--White----Black

 

You could verify that there's +12 volts on the original red (yellow/red) lead after starting the engine, which would be the heater supply/hot (the white should be the heater return/ground, switched by the ECU). Since the heater itself doesn't care about polarity, it would make sense that the replacement sensor's heater leads would both be the same color (black in this case).

 

EDIT: Some early-90's cars used titania (not zirconia) oxygen sensors, and had black-red-white wires. Are you sure that the replacement is correct?

Edited December 14, 200916 yr by OB99W

slightly off topic but very informative:

 

 

how does an o2 sensor work, including how to test an o2 sensor, click here

 

 

 

 

 

 

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Thanks guys......I will be "wiring it up" tomorrow!

 

Todd