DTC P0138 (2020 2021): 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 from the air/fuel ratio (A/F) sensor (sensor 1) output voltage to optimize the TWC efficiency. When power is applied to the secondary HO2S (sensor 2) heater, if the secondary HO2S (sensor 2) output voltage is high or the SO2SG terminal voltage is high during feedback control, the PCM detects a malfunction and stores a DTC.