Q: o2 sensor reads 0 volts.

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I have a 2000 Ford Mustang v6 3.8L with a P0122, but the code isn't the main issue. The freeze frame data shows that the B1S2 oxygen sensor reads 0 volts.

To verify the o2 sensor works, I switched the two downstream sensors. I still have the same problem. The problem didn't move with the sensor.

To verify the wiring, I plugged the B1S2 harness into the B2S2 o2 sensor and it worked plugged into the other side of the car.

So, with the sensor and wiring harness verified, I'm forces to believe that the 0 volts is accurate. Could it be that all three cylinders on bank1 are misfiring resulting in no exhaust and 0 volts measured by the o2 sensor?

The freeze frame data shows 0 volts but when I graph the o2 sensor, it shows between .02 and .04.

The car idles rough. It's also rough when I press the accelerator while idling. I don't notice it when I drive it.

NOTE: The left and right exhaust manifolds and the Y-exhaust pipe were replaced last month due to a previous P0171 code.

You may need to look at the code P0122 since it pertains to the throttle position sensor and this can affect all the drive symptoms you are having. The O2 sensor readings seem to be normal and you are not getting any O2 sensor codes. Your reading of between .2 and .4 volts shows that the converter is doing its job and you have high O2 in the exhaust flow. This is a common and normal reading. When the catalyst is new you may not see the O2 sensor go above .45 volts but as a catalyst ages the sensor will switch more often above the .45 volts until it cannot clean the exhaust anymore. I’d suggest getting some help with a certified technician, such as one from YourMechanic, they will help you diagnose your Check Engine Light further and help you fix it accordingly.

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