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 tests rear HO2S signal level during the time the lambda target point is being shifted to rich to determine rear HO2S signal stuck. The PCM sets DTC P2270 if rear HO2S signal is below the predetermined threshold while target lambda point is being shifted to the predetermined value. If the same error code is set in the next driving cycle, the PCM illuminates the MIL.
Item
Detecting Condition
Possible cause
DTC Strategy
Downstream O2 sensor signal too low
Poor connection or damaged harness
Rear HO2S
Enable Conditions
No fuel cut-off
No full load phase
No catalyst overheating protection
11V < Battery voltage < 16V
Threshold value
Rear HO2S signal < 0.75V when lambda set point = 0.80
Diagnosis Time
7 sec after lambda set point shift to corresponding side
MIL On Condition
2 driving cycle
? Sector A : Signal Normal
? Sector B : Signal Fluctuation
? Sector C : Signal Recovery