DTC P0138: Ho2S (Rear) Circuit, High Input: Condition
WARNING: This page is about a different car, the 2002 Mazda Protege5 and 2002 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.
DTC is set when rear HO2S input is more than .45 volt for 6 seconds during decelerations (fuel cut). This is a continuous monitor. MIL is illuminated when PCM detects malfunction during 2 consecutive drive cycles. Possible causes are:
- Rear HO2S malfunction.
- Short circuit between rear HO2S and PCM.