Drive with caution — fix soon.
This code means the engine isn't reaching the temperature it needs to switch into closed-loop fuel control, where the computer uses oxygen sensor data to fine-tune fueling. Until that happens, the engine runs richer and less efficiently. The most common cause is a thermostat stuck open or a faulty coolant temperature sensor.
$100 – $350
Varies by vehicle and root cause.
Usually yes, but expect worse fuel economy and a weak heater. It's not an emergency, though a stuck-open thermostat should be replaced soon to restore proper operation.
Often $100 to $350, depending on the cause. Replacing a thermostat is moderate; a sensor swap can be cheaper, while harder-to-reach parts cost more in labor.
It's a moderate concern. The car still runs, but staying out of closed-loop wastes fuel and increases emissions, so it's worth fixing.
Most often a thermostat is stuck open, letting coolant flow constantly so the engine never reaches operating temperature. A faulty temperature sensor can also trigger the code.