General Information

Engine Control

P0139 O2 Sensor Circuit Slow Response (Bank 1 / Sensor 2) - General Information

Component Location





General Description

The rear heated oxygen sensor is mounted on the rear side of the Catalytic Converter (warm-up catalytic converter) or in the rear exhaust pipe, which is able to detect catalyst efficiency. The rear heated oxygen sensor (HO2S) produces a voltage between 0 V and 1 V. This rear heated oxygen sensor is used to estimate the oxygen storage capability. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to aging, poisoning or misfiring, then the oxygen fluctuations are similar to signals from the front oxygen sensor.

DTC Description

Checking output signals from HO2S under detecting condition, if ECM judges it's signals too slow, ECM sets P0139. The MIL (Malfunction Indicator Lamp) will illuminate when the fault remains for 2 consecutive drive cycles

DTC Detecting Condition





Specification

(Reference only)






Diagnostic Circuit Diagram





Signal Waveform & Data








Fig.1) Normal waveforms of front HO2S (the upper) and rear HO2S (the lower). (Waveform between HIGH signal line of HO2S and chassis ground)
Fig.2) Normal graph of front HO2S and rear HO2S at idle.

After warming-up, if accelerator pedal is released suddenly around 4000 rpm, the HO2S signal reading will be lower than 200 mV resulting from Fuel cut-off for the moment. Conversely, if suddenly accelerator pedal is depressed, HO2S signal reading will be around 0.6 V ~1.0 V. At idle, Normally HO2S signal will switch from lean to rich with 3 Hz. And as racing, Its frequency rises.