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.
ECM set P2271 code if output signal is too high at DOWN O2 sensor when AIR-FUEL ratio is under rare condition.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
No signal activity | 1. Poor connection 2. Short to Power in signal circuit 3. HO2S(B1/S2) 4. ECM |
Enable Conditions |
•
Battery voltage > 10.7V
•
Lambda = 1.1 for 9 sec | |
Threshold Value |
•
Downstream O2S voltage > 0.65V | |
Diagnostic Time |
•
9 sec | |
MIL ON Condition |
•
2 Driving Cycles |
The amplitude of the signal output of the rear HO2S is small compared to the front HO2S because the rear HO2S detects emission gas purified by the catalytic converter. This is the normal signal waveform of the rear HO2S at idle.
