* Fuel Pump Issues: When the fuel level gets very low, the fuel pump may be drawing air, causing it to work harder and potentially overheat or malfunction. This can trigger a diagnostic trouble code (DTC) that results in the Service Engine Soon light illuminating.
* Fuel Level Sensor Malfunction: A faulty fuel level sensor might report an inaccurate fuel level, which could, in extreme cases, trigger a related DTC and illuminate the Service Engine Soon light, especially if it's misreporting the level as critically low even when it's not.
* Other related issues masked by low fuel: Sometimes, a different underlying problem (like a faulty mass airflow sensor or other fuel system issue) may only become apparent when the fuel level is low and the engine has to work harder to compensate.
In short, a low fuel level doesn't *cause* the Service Engine Soon light, but it can create conditions that trigger problems, which in turn trigger the light. It's always best to fill your tank to avoid potentially stressing the fuel system, and to get the car diagnosed to find the actual cause of the Service Engine Soon light rather than simply filling the tank.
