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Old 12-07-2017, 02:46 PM   #1
Greasyjonny
Scooby Newbie
 
Member#: 478765
Join Date: Dec 2017
Location: MA
Vehicle:
2007 Impreza wagon

Default Voltage at upstream o2 sensor conection?

07 Impreza Wagon, 130k Miles

Chasing down a p0031. Heated circuit on bank 1 sensor 1 faulty/low voltage. I checked all the fuses in the engine bay, and all are in tact. The next thing I wanted to check before swapping with new sensor is the voltage at the connector to ensure there isnít a wiring problem elsewhere. Iím new to this so Iím not sure if I tested it correctly, but I removed the sensor from the connector, put the car in start (not running) and checked the voltage at each prong in the connector (4 wire connector). I got a 12v, a 0, 2.4 and 2.8 volts. Iím not sure what a proper reading should be and Iíve been scouring the internet for days. Any help would be appreciated.
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Old 12-11-2017, 03:32 PM   #2
IanT-EJ22
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Member#: 477892
Join Date: Nov 2017
Default

12 volts is good, that means your harness is getting power from the ecu for the supply to the heater portion of the sensor (grey wire). There should be 0 volts @ the connector for the ground to the heater portion of the sensor (one of the white wires). One of the other two (2.4v and 2.8v) readings you got was the (+) supply to the air/fuel circuit and the other reading is a wire that is the ground for the air/fuel circuit portion of the sensor. The heater circuit uses the two white wires, the air/fuel a grey and a black.

I think your good, heater circuits in H02s tend to go bad after not all that long. They are fragile and are exposed to alot of abuse by high heat, moisture and vibration.
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