Grand Caravan FWD V6-3.0L VIN 3 (1999)
Heated Oxygen Sensor
The upstream O2S is located in the exhaust manifold and provides an input voltage to the PCM. The input tells the PCM the oxygen content of the
exhaust gas. The PCM uses this information to fine tune the air/fuel ratio by adjusting injector pulse width.
DOWNSTREAM HEATED OXYGEN SENSOR
Downstream Heated Oxygen Sensor
The downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic convertor. The downstream heated oxygen sensor
input is used to detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream sensor begins to match the
upstream sensor input except for a slight time delay. By comparing the downstream heated oxygen sensor input to the input from the upstream
sensor, the PCM calculates catalytic convertor efficiency.
When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic trouble code and illuminates the Malfunction
Indicator Lamp (MIL). For more information, refer to Emission Control Systems.
