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Hello,
My first post here so please be gentle.....
Working on a 1998 Legacy Outback. 2.5L, manual. The engine is not the original.
Starts and runs well, but Check Engine is on. Codes indicate both O2 sensors. This makes sense, because both sensors are not connected!
The rear sensor does not have a plug any longer. Just three wires hanging loose. Black and two whites. The two whites = heater, right? (No polarity on these - right?) and black = signal? The wiring harness has the plug with 3 wires. I think I can sort out this end. Find +12Volts & ground for the heater and the black goes to black for the signal.

The front is a problem. The sensor has a 4 wire plug - (2) white, (1) black & (1) grey. The wiring harness has a 3 pin plug - kind of a triangular shape roughly speaking. Colors look like white/red, white and black. (Hard to tell.) The engine must be from a different year or different vehicle and the harness doesn't match the sensor.

Engine is number: 475746. Any idea what this is from?
Am I correct in thinking if I can get an OEM sensor that matches the engine and screw it into the exhaust (same threads hopefully??) that all should work OK?

Thanks for reading this long post...
 

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Discussion Starter #2
More information....
What I thought was a black wire on the rear harness is actually a green/white wire at the connector that transitions into a black shielded wire further up the harness.
Dennis
 

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Talking to myself here.....
After more thought, I realized the problem must be the front sensor in the exhaust and not the engine. Even if the engine was changed, the wiring harness would not have been changed. Therefore the "triangle" shaped, three wire connector must be correct one for the vehicle.

Tried to wire in the four wire sensor using the black as a signal and grounding the grey wire. (Also connected the two white wires for the sensor's heater.) With the black wire connected and the grey wire grounded, the car ran for schite. Stumbling and undriveable.

With the sensor unplugged it runs good. Time to get a new OEM front sensor...
Dennis
 

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Sorry I didn't notice this sooner- long history of non-OEM sensors causing problems in subarus. You can get away with the cheaper generics in the rear position but not for the front.
 
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