DTC P0138:00: Notes

DTC P0138:00	HO2S circuit high input
DETECTION CONDITION	The PCM monitors input voltage from HO2S. If the input voltage from the HO2S is above 1.2 V or HO2S bias voltage above 1.7 V for 5 s , the PCM determines that the HO2S circuit input is high. Diagnostic support note This is a continuous monitor (A/F sensor, HO2S). The check engine light illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. PENDING CODE is available if the PCM detects the above malfunction condition during first drive cycle. FREEZE FRAME DATA (Mode 2)/Snapshot data is available. The DTC is stored in the PCM memory.
FAIL-SAFE FUNCTION	-
POSSIBLE CAUSE	HO2S connector or terminals malfunction PCM connector or terminals malfunction Short to power supply in wiring harness between HO2S terminal A and PCM terminal 2Q HO2S circuits are shorted to each other HO2S malfunction PCM malfunction
Courtesy of MAZDA MOTORS CORP.