Sensor, Oxygen: Description

The Oxygen Sensors (O2S) are attached to, and protrude into the vehicle exhaust system. Depending on the engine or emission package, the vehicle may use a total of either 2 or 4 sensors.

Federal Emission Packages :  Two sensors are used: upstream (referred to as 1/1) and downstream (referred to as 1/2). With this emission package, the upstream sensor (1/1) is located just before the main catalytic convertor. The downstream sensor (1/2) is located just after the main catalytic convertor.

California Emission Packages:  On this emissions package, 4 sensors are used: 2 upstream (referred to as 1/1 and 2/1) and 2 downstream (referred to as 1/2 and 2/2). With this emission package, the upstream sensor (1/1) is located in the exhaust of the leading cylinder bank just before the mini-catalytic convertor. The other upstream sensor (2/1) is located in the exhaust of the opposite cylinder bank just before the mini-catalytic convertor. The downstream sensor (1/2) is located in the exhaust downpipe of the leading cylinder bank, just after the mini-catalytic convertor and before the main catalytic convertor. The other downstream sensor (2/2) is located in the opposite exhaust downpipe just after the mini-catalytic convertor and before the main catalytic convertor.