Wrangler 4WD L4-150 2.5L VIN P MFI (1998)
The downstream heated oxygen sensor is located near the outlet end of the catalytic convertor (Fig. 6). The downstream heated oxygen sensor
input is used to detect catalytic convertor deterioration and provide fuel adjustment information.
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 (MIL) (or Check Engine) lamp. For more information, refer Emission Control Systems.
The downstream sensor input is also used to adjust the upstream O2S goal voltage. This allows a better control of the exhaust gases as the catalytic
convertor ages.
NOTE: The upstream and downstream sensors may look exactly alike, but are not interchangeable.
CIRCUIT OPERATION
When the Automatic Shut Down (ASD) relay contacts close, they connect circuits A14 and A142. Circuit A142 splices to supply voltage to the
upstream and downstream heated oxygen sensors.
Circuit K41 delivers the signal from the upstream heated oxygen sensor to the Powertrain Control Module (PCM). Circuit K41 connects to cavity
A24 of the PCM. Circuit K141 supplies the signal from the downstream heated oxygen sensor to the PCM. Circuit K141 connects to PCM cavity
A25.
The PCM provides a ground for the heated oxygen sensor signals (circuits K41 and K141) through circuit K167. Circuit K167 connects to cavity
A4 of the PCM connector.
Circuit Z1 provides ground for the heater circuit in each sensor.
