DTC P0136: O2 Sensor Circuit (Bank 1/Sensor 2): General Description

The rear Heated Oxygen Sensor (HO2S) downstream (S2) is on the rear side of Catalytic Converter, and it is used to check the proper operation of the catalyst. The oxygen density after the catalytic converter has to be within specific range (around 0.5V when there is no acceleration/deceleration). This sensor is used to estimate the oxygen storage capability. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to aging, poisoning or misfiring, then the oxygen fluctuations are similar to signals from the front oxygen sensor.