The oxygen sensor in your Toyota Corolla is a electronic component that senses the amount of oxygen entering your car's engine and sends this data to the on-board computer so the proper amount of fuel is sent to the engine. If the oxygen level measurement is off, too little or too much fuel is sent to your engine, and your car will run erratically. The oxygen sensor is a key component in your Corolla. When the device is not functioning correctly, symptoms do present themselves.
Poor Gas Mileage
One symptom of a bad oxygen sensor is your Corolla using an excessive amount of gas. The sensor is not sending the correct oxygen reading to the computer--or not sending a reading at all--so the on-board computer sends too much fuel to your Corolla's engine.
Gas & Exhaust Smells
You will notice a strong gas and rotten egg smell coming from your car's engine and exhaust system. This is due to the excessive amount of fuel being sent to your Corolla's engine. The smell will be present on the outside of your car as well as the inside.
Another symptom of a bad oxygen sensor is running rough, including shaking; idle surging when your car is in "Park" or "Drive"; the engine cutting off when you reach a stop sign or red light; misfiring at idle and while you are driving your Carolla; and taking a long time to crank when the engine is cold.
If equipped, the "Oxygen Sensor" light will illuminate on your Corolla's dashboard as well as the "Service Engine Soon" or "Check Engine" light.
Failing Emissions Test
The oxygen sensor is a component of your car's emission system. If your state requires that you take your car to an emission inspection station, a bad sensor will cause your car to fail the emissions test.