Q: P0171 bank 1 upstream O2 sensor

Hello, thank you for writing in. The bank 1 upstream oxygen sensor is referring to the oxygen sensor that is before the catalytic converter. If looking at the exhaust system, it would be located on the main pipe between the engine and the catalytic converter. This is the first oxygen sensor in which the second oxygen sensor relates its readings to. If the sensors vary, the issue may be the catalytic converter, or a failed oxygen sensor. Build up and contamination will also give a false reading. To locate the sensor, trace the tailpipe from the engine towards the cat. You will see the wires coming from it. It should stand out as there are no other sensors on the pipe in that area. For more help servicing the oxygen sensors contact our service department.