- The upstream (pre-catalytic converter) oxygen sensor is located in the exhaust manifold.
- The downstream (post-catalytic converter) oxygen sensor is located in the exhaust pipe, just after the catalytic converter.
1997-1998:
- The E250 has two oxygen sensors: a heated oxygen sensor (HO2S) and a downstream oxygen sensor (DO2S).
- The HO2S is located in the exhaust manifold, just upstream of the catalytic converter.
- The DO2S is located in the exhaust pipe, just downstream of the catalytic converter.
1999-2014:
- The E250 has two oxygen sensors: a front oxygen sensor (FO2S) and a rear oxygen sensor (RO2S).
- The FO2S is located in the exhaust manifold, just upstream of the catalytic converter.
- The RO2S is located in the exhaust pipe, just downstream of the catalytic converter.
