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