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Code Enable Criteria

Engine is running.
HO2S12 is in closed loop.
Fuel level is more than 10 percent.
Calculated catalytic converter temperature is less than 1724°F (940°C).
Commanded air/fuel ratio is 14.7:1.
Battery voltage is more than 11 volts.
No EGR or EVAP DTCs are set.

DTC sets when HO2S12 voltage is less than 40 millivolts for more than 80 seconds.