I can't seem to figure this one out. I keep getting p0138 high voltage in after cat O2 sensor signal wire because I have over 10volts in it for whatever reason...

- Car running O2 sensor plugged in, I get 10.5 volts
- Car running O2 sensor unplugged, I have 11.5volts
- Engine OFF or engine OFF but ignition ON, no voltage.

All measured at ECU (ECU pin 75 rear o2 sensor signal wire)

I can't figure out why this is happening. O2 sensors should only make 0.1 to 0.9 volts roughly when the car is warm, seeing even 2volts in this wire isn't normal...

Anyone have any suggestions?? I'm out of ideas
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PS after much testing I never did figured out why I have such high voltage in this wire (do still tell if anyone has any ideas still) but I was able to get rid of the p0138 by disabling secondary 02 in ecuflash Periperty0, bit2
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I think there is only one connector in the rear O2 oxygen sensor circuit, located on the floorboards somewhere. The cable is four wire, the other two wires for the heater, 12 volts and ground. Anyway, it being winter still, meaning salty wet floor mats, I'm wondering if water could have gotten into the connector shorting the sensor to battery voltage.

 

I checked the connector, and I even did the test with the rear 02 disconnected at the passenger seat connector and the 02 still shows the p0138 voltage too high. I even tested the signal wire at the ECU with the o2 disconnected completely and the signal wire still shows 11.5 volts. If the 02 is unplugged this wire should not have any voltage.
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