Code P0138 HO2S2 Nissan Dualis, Qashqai HR16DE

The heated oxygen sensor 2, after three way catalyst (manifold),monitors the oxygen level in the exhaust gas on each bank.Even if switching characteristics of the heated oxygen sensor 1 areshifted, the air-fuel ratio is controlled to stoichiometric, by the signalfrom the heated oxygen sensor 2.This sensor is made of ceramic zirconia. The zirconia generates volt-age from approximately 1V in richer conditions to 0V in leaner condi-tions.Under normal conditions the heated oxygen sensor 2 is not used forengine control operation.

DTC DETECTION LOGIC The heated oxygen sensor 2 has a much longer switching time between rich and lean than the heated oxygensensor 1. The oxygen storage capacity of the three way catalyst (manifold) causes the longer switching time.To judge the malfunctions of heated oxygen sensor 2, ECM monitorswhether the voltage is unusually high during the various driving con-dition such as fuel-cut.