DTC P0139: General Description
The rear secondary heated oxygen sensor (secondary HO2S (bank 1, sensor 2)) detects the oxygen content in the exhaust gas downstream of the rear warm up three way catalytic converter (WU-TWC) (bank 1) during stoichiometric air/fuel ratio feedback control. The powertrain control module (PCM) controls the air/fuel ratio with the rear air/fuel ratio (A/F) sensor (bank 1, sensor 1) output voltage to optimize the rear WU-TWC (bank 1)'s efficiency. When the rear secondary HO2S (bank 1, sensor 2) does not change during lean air/fuel ratio when the throttle is closed, after full current is applied to the rear secondary HO2S (bank 1, sensor 2) heater, and output remains within the specified range continuously, the PCM detects a malfunction and stores a DTC.