Onda and Acura vehicles between 2009 and 2012, a "Pack of 4" oxygen (O2) sensor set typically includes two upstream (Bank 1 Sensor 1 and Bank 2 Sensor 1) and two downstream (Bank 1 Sensor 2 and Bank 2 Sensor 2) sensors. These packs are primarily designed for models with V6 engines, such as the 3.5L or 3.7L, which require four sensors to monitor both cylinder