Oxygen Sensor Location & Identification

This article provides information on the proper identification of engine bank 1 and engine bank 2 for correct oxygen sensor replacement.

This information identifies engine bank 1 and engine bank 2 on the following engine emission packages:

• Bank 1 refers to the cylinder bank that includes cylinder No. 1.
• Bank 2 refers to the cylinder bank opposite bank 1.
• Sensor 1 refers to the sensor that is located before the catalytic converters.
• Sensor 2 refers to the sensor that is located after the catalytic converters.

For cylinder identification, refer to FIRING ORDER & CYLINDER IDENTIFICATION article.

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 converter. The downstream sensor (1/2) is located just after the main catalytic converter

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 left upstream sensor (2/1) is located in the left exhaust downpipe just before the mini-catalytic converter. The right upstream sensor (1/1) is located in the right exhaust downpipe just before the mini-catalytic converter. The left downstream sensor (2/2) is located in the left exhaust downpipe just after the mini-catalytic converter, and before the main catalytic converter. The right downstream sensor (1/2) is located in the right exhaust downpipe just after the mini-catalytic converter, and before the main catalytic converter.