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 0V and 1V. 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.
The PCM monitors rich-lean switching time of rear heated oxygen sensor (HO2S) after fuel cut-off to validate dynamic behavior of rear heated oxygen sensor (HO2S). After detection of fuel cut-off engine operating state, the PCM measures rich-lean switching time of the rear heated oxygen sensor (HO2S) signal and compares it to the predetermined limit value. DTC P0139 is set when the switching time is bigger than the limit value.
ITEM | DETECTING CONDITION | POSSIBLE CAUSE |
DTC Strategy | ● Slow response(Switching time check at entry in fuel cut off) | ● Leak in intake or exhaust system ● Faulty fuel system. ● Front and rear HO2S connections reversed. ● Contact resistance in connectors ● HO2S contamination |
Enable Condition | ● Coolant temp ＞74°C(165°F) ● Closed loop mode ● 5km/h(3mph) ＜ Vehicle speed ＜ 180km/h(112mph) ● Sensor preheating and full phase finished ● Catalyst temp.model ＞350°C(662°F) ● No relevant failure ● 11 ＜ Battery voltage ＜ 16 ● Downstream O2 sensor signal at entry in fuel cut off ＞ 0.55V | |
Threshold Value | ● Average ratio(between measured and maximum allowed switching time at entry in fuel cut-off) ＞ 1 | |
Diagnostic Time | ● 5 fuel cut-off phases |
