OBD-II Heated Oxygen Sensor Numbering Convention

ALLDATA Editor's Note: Always verify #1 cylinder location prior to diagnosis and repair.

- Cylinder bank number one is the bank that contains number one cylinder.


Firing Order





Cylinder #1 on left side.




Cylinder #1 on right side.

- The first oxygen sensor in cylinder bank # 1 is numbered O2 Sensor 1/1.
- The second oxygen sensor in cylinder bank # 1 is numbered O2 Sensor 1/2.
- A third oxygen sensor in cylinder bank # 1 would be numbered O2 Sensor 1/3.
- The first oxygen sensor in cylinder bank # 2 is numbered O2 Sensor 2/1.
- The second oxygen sensor in cylinder bank # 2 is numbered O2 Sensor 1/1.



- If a V-6 or V-8 vehicle only uses one downstream Heated Oxygen Sensor (HO2S) it is numbered O2 Sensor 1/2, even if it uses two upstream HO2S.