Enhanced Testing

P0138 - HO2S Circuit High Voltage (B1/S2)






General Description
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 detects the 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.


DTC Description
If HO2S signal voltage has continued to exceed 1.2 volts, the ECM determines that a fault exists and a DTC is stored.

Detecting Condition and Specifications





Wiring Schematic





Signal Waveform