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 sets DTC P0138 if the HO2S(B1S2) voltage remains excessively high for a predetermined time
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Voltage range check | ● Short to Battery in signal harness ● Contact resistance in connectors ● Faulty Heated O2 Sensor(HO2S) |
Enable Conditions | ● 10 < Battery voltage < 16V | |
Threshold Value | ● Sensor voltage >1.3V | |
Diagnostic Time | ● 1 sec. | |
MIL On Condition | ● 2 Driving Cycles |
Test Condition | Scan Tool Parameter | ||
O2 SNSR VOL.-B1/S1 | O2 SNSR VOL.-B1/S2 | ||
Normal Value when circuit is normal | Idle after warm up | Signal is switching from rich(above 0.45V) to lean(below 0.45V) a minimum of 3 times in 10 seconds. | above 0.7V |
HO2S(B1S1) signal circuit open | Approx. 0.43~0.45V | - | |
HO2S(B1S2) signal circuit open | - | Approx. 0.43~0.45V | |
