General Information

Engine Control
P0138 O2 Sensor Circuit High Voltage (Bank 1 / Sensor 2) - General Information

Component Location





General Description

HO2S(S2) is in the rear side of Catalytic Converter to check the proper operation of catalyst. Oxygen density after the catalytic converter has to be within specific range (around 0.5V when there is no acceclation and deceleration.)
If the oxygen density changes in accordance with HO2S(S1), it means the poor performance of catalytic converter.

DTC Description

If the sensor output is over 1.08 V under enable conditions, ECM sets DTC P0138.
(This DTC might be caused by the malfunction of Heater circuit, so, check the heater circuit first. )

DTC Detecting Condition





** S1 : upstream oxygen sensor / S2 : downstream oxygen sensor

Diagnostic Circuit Diagram










Signal Waveform & Data




The amplitude of the signal output of the rear HO2S is small compared to the front HO2S because the rear HO2S detects emission gas purified by the catalytic converter. This is the normal signal waveform of the rear HO2S at idle.