Grand Cherokee 4WD Laredo V8-4.7L (2002)
from the # 1 cylinder. They provide 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 fuel delivery to maintain the correct oxygen content at the downstream oxygen sensors. The PCM will change the
air/fuel ratio until the upstream sensors input a voltage that the PCM has determined will make the downstream sensors output (oxygen content)
correct.
The upstream oxygen sensors also provide an input to determine mini-catalyst efficiency. Main catalytic convertor efficiency is not calculated with
this package.
Downstream Sensors (California Engines): Two downstream sensors are used (1/2 and 2/2). The downstream sensors are used to determine the
correct air-fuel ratio. As the oxygen content changes at the downstream sensor, the PCM calculates how much air-fuel ratio change is required.
The PCM then looks at the upstream oxygen sensor voltage, and changes fuel delivery until the upstream sensor voltage changes enough to correct
the downstream sensor voltage (oxygen content).
The downstream oxygen sensors also provide an input to determine mini-catalyst efficiency Main catalytic convertor efficiency is not calculated
with this package.
Engines equipped with either a downstream sensor(s), or a post-catalytic sensor, will monitor catalytic convertor efficiency. If efficiency is below
emission standards, the Malfunction Indicator Lamp (MIL) will be illuminated and a Diagnostic Trouble Code (DTC) will be set. Refer to
Monitored Systems in Emission Control Systems for additional information.
