O2 Sensor: Description

The upstream O2 sensors are in the exhaust system in the exhaust manifold collector area before the upstream catalytic convertor. See Fig 1.

Fig 1: 2/1, 2/2, O2 SENSORS

Courtesy of DAIMLERCHRYSLER CORP.

1 - Upstream O2 Sensor

2 - Downstream O2 Sensor

The downstream O2 sensors are in the exhaust system in between the catalytic convertors. See Fig 1.