Some 2011 Mazda vehicles built before Feb. 9, 2011, may experience MIL illumination with DTC P0128 (thermostat stuck open) stored in memory during engine warm-up at idle. This may be caused by the thermostat jiggle pin contacting the thermostat cover because the thermostat jiggle pin location was not oriented properly.
Remove the thermostat and check if the jiggle pin is positioned at the top. Perform thermostat inspection referring to the MS3 online or workshop manual. If thermostat inspection shows failure, replace the thermostat. When installing the thermostat, be sure to place the jiggle pin at the top (12 o’clock position). Tighten the thermostat cover bolts to 15-18 ft.-lbfs.