Except California Emission Regulation Applicable ATX Model: Notes

DTC P0031 DETECTION CONDITION AND POSSIBLE CAUSES

DTC P0031	Front HO2S heater circuit low input
DETECTION CONDITION	The PCM monitors the front HO2S heater output voltage, if the PCM turns the front HO2S heater off or on but the front HO2S heater circuit remains low voltage, the PCM determines that the front HO2S heater circuit has a malfunction. NOTE: The front HO2S heater is controlled by duty signal. Diagnostic support note  This is an intermittent monitor (HO2S heater). The MIL 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 the first drive cycle. FREEZE FRAME DATA is available. The DTC is stored in the PCM memory.
POSSIBLE CAUSE	Front HO2S heater malfunction Connector or terminal malfunction Open circuit in wiring harness between ignition switch and front HO2S terminal 2B Short to ground in wiring harness between ignition switch and front HO2S terminal 2B Open circuit in wiring harness between front HO2S terminal 2D and PCM terminal 2BG Short to ground in wiring harness between front HO2S terminal 2D and PCM terminal 2BG PCM malfunction
Courtesy of MAZDA MOTORS CORP.