With Coolant Control Valve

DTC P0031:00 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P0031:00	A/F sensor heater control circuit low input
DETECTION CONDITION	When the PCM controls the A/F sensor heater, the voltage input to the PCM is too low. Diagnostic support note This is a continuous monitor (A/F sensor heater, HO2S heater). 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/Snapshot data is available. DTC is stored in the PCM memory.
FAIL-SAFE FUNCTION	Stops fuel feedback control
POSSIBLE CAUSE	A/F sensor connector or terminals malfunction Short to ground or open circuit in A/F sensor heater power supply circuit: Short to ground in wiring harness between ENGINE2 15 A fuse and A/F sensor terminal A ENGINE2 15 A fuse malfunction Open circuit in wiring harness between sub relay terminal C and A/F sensor terminal A A/F sensor heater malfunction PCM connector or terminals malfunction Open circuit in wiring harness between A/F sensor terminal E and PCM terminal 1CB Short to ground in wiring harness between A/F sensor terminal E and PCM terminal 1CB PCM malfunction
Courtesy of MAZDA MOTORS CORP.