Q: Oxygen sensor issue - 3.8LT V6 P0151 voltage low bank 2 sensor 1 2004 Holden Commodore

Hello - the P0151 code, as you have noted. Assuming the new O2 sensor is a good one, the problem could be faulty wiring to the sensor, an air leak in the intake, or a malfunctioning Mass Air Flow (MAF) sensor - which you have cleaned. For assistance with further diagnosis, I recommend a Check Engine inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.