The oxygen sensors used on a Wrangler play an important role in engine efficiency and environmental pollution. Their purpose is to read the amount of oxygen content left in the exhaust and report back to the ECU, which then, in turn, will change the fuel mixture in order to maintain a proper air-to-fuel ratio (the ideal ratio is 14.7 parts air to 1 part fuel - 14.7:1). Through the feedback loop of the oxygen sensors, the ECU is able to keep the AFR within tight limits which promotes engine efficiency and power delivery.
The oxygen sensors equipped on JK and JL Wranglers use a Zirconia element (coated both inside and out with a layer of platinum to act as an electrode) that is capable of conducting oxygen ions when at or above 350 C. With the sensor installed in the downpipe, the exterior element is exposed to the exhaust stream whereas the inner area is exposed to air. When at operating temperature, the remaining oxygen molecules from the exhaust are able to pass through the zirconia sensor element and deposit a charge on the interior platinum electrode which then generates a voltage. This voltage is measured by the ECU and depending on its value, fuel trim is either increased or decreased.
A low voltage indicates that the engine is running lean and the AFR is too high whereas a high voltage indicates a rich mixture and that fuel should be removed from the combustion process.
A faulty or inoperative oxygen sensor will illuminate the Check Engine Light and can have detrimental effects on fuel economy and power delivery as now the ECU will not be supplying the proper amount of fuel in order to maintain an AFR of 14.7. On top of this, due to the improper mixture, combustion pollutants will increase. Oxygen sensors do wear out due to the heat cycles and road grime they are exposed to. Most manufacturers call for an oxygen sensor to be replaced every 100,000 miles. Jeep Wranglers use a four-wire ISO-HEGO (isolated heated exhaust gas oxygen sensor) unit.