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P0138 - Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)
Fault codes never say to replace parts. They only indicate the circuit or system that needs further diagnosis. The only way to set this code is to have a break in the sensor's ground wire or the signal voltage wire is shorted to the 12 volt heater wire for that sensor. Start by looking for a corroded terminal in the sensor's connector or a terminal that got stretched or pushed out of the plug body. Next, check the wiring harness for signs of melted wires, especially where they travel near hot exhaust parts.
If you haven't found the cause by this time, use a scanner to view live data and look at the sensor's voltage compared to the passenger side sensor. If it's normal, you have an intermittent problem that isn't currently acting up. Try flexing on the wire harness to see if the voltage changes. If the voltage IS high, unplug connectors going to that sensor and wiggle harnesses until the voltage changes. That will help you narrow down the location of the problem.
Bank 1 is where cylinder number 1 is located, being sensor 2 this is the downstream sensor or the catalytic monitor sensor. Voltage high means the sensor signal or the return signal are shorted to ground.or the 02 sensor is disconnected, check the mating connection or the harness for proper mating , and harness being shorted.
Hey, The o2 sensor affects the fine tuning of the engine. it is used to tell how well the engine is burning off the fuel in the combustion process. if there is too much oxygen, then it will adjust the air/fuel mixture accordingly and vice versa. If the car runs too lean or to rich you will loose power and possibly damage your engine. It would be a good idea to replace if its faulty.
I would be inclined to say it is electrical in nature. Did you set the spark plug gap at .050? It is possible you could have a bad plug wire. Where did you get the DTCs from? GM service shop? #7 cylinder is on the rear head. Check wiring again just to eliminate that possibility. As a last ditch effort, get the GM shop to DIAGNOSE your problems, and then fix it yourself. Again, I think the source is electrical, but it is possible, although unlikely you could have a fuel problem, but no fuel DTCs are showing. I assume the MIL on the dash is lit.