OBD-II Heated Oxygen Sensor Numbering Convention

HO2S Locations:

The first oxygen sensor in cylinder bank #1 is numbered HO2S11.
The second oxygen sensor in cylinder bank #1 is numbered HO2S12.
The first oxygen sensor in cylinder bank #2 is numbered HO2S21.
The second oxygen sensor in cylinder bank #2 is numbered HO2S22.

- Cylinder bank number one is the bank that contains number one cylinder.
- If a V-6 or V-8 vehicle only uses one downstream Heated Oxygen Sensor (HO2S) it is numbered HO2S12, even if it uses two upstream HO2S.