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.
Checking output signals from HO2S under detecting condition, if an output signal within the detecting condition lasts continuously, PCM sets P2272. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item
Detecting Condition
Possible cause
DTC Strategy
? Determines if O2 sensor indicates lean exhaust while in Power Enrichment
? Poor Connection
? Faulty HO2S
? Faulty PCM
Enable Conditions
? Sensor not in cooled status
? Not in Transient Conditions status
? Airflow present = 2 g/s
? Ignition voltage = 10V
? Fuel reduction not active
? Engine running
? Engine running long enough = 60sec.
? Power Enrichment conditions present
? Engine coolant warm enough = 60°C( 140 °F)
? Above conditions met long enough = 2.5sec.
Threshold value
? O2 sensor voltage < 0.54V and, Air Fuel Ratio = 13.5
Diagnosis Time
? Contineous (More than 11.25sec. failure for every 12.5sec. Test)
MIL On Condition
? 2 Driving Cycles
A/F Ratio
Output Voltage(V)
Rich
0.75 ~ 1.00V
Lean
0 ~ 0.12V