General Information

P0139 O2 Sensor Circuit Slow Response (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 0.5 V when there is no acceleration and deceleration.) If the oxygen density changes in accordance with HO2S (S1), it means the poor performance of catalytic converter.

DTC Description

ECM checks output signals from HO2S under detecting condition. ECM judges it's signals too slow and sets P0139, if output signal from rear HO2S isn't increased up to specification level within a short time after fuel cut. (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 and Data




If you release the accelerator pedal suddenly after engine running about 4000 rpm, fuel supply will stop for short period and the O2 sensor service data in the Hi-Scan (Pro) will display values 200 mV or lower. When you suddenly press on the accelerator pedal down, the voltage will reach 0.6 - 1.0 V. When you let the engine idle again, the voltage will fluctuate between 200 mV or lower and 0.6 - 1.0 V. In this case, the O2 sensor can be determined as good.