If you've ever looked under the hood of your Toyota Celica, you might have noticed a component sticking out into your car's exhaust stream, about the same size and shape as a spark plug. You might have noticed more than one. These are your factory oxygen sensors. Their job: to determine whether the oxygen levels in your exhaust are correct. This way, your engine can adjust its fuel use for optimum efficiency. Unfortunately, oxygen sensor failure is common; its cause can be nothing more than your sensors getting dirty because of spent motor oil or impurities in your gas. When to replace an oxygen sensor, then, is straightforward: newer ones can last up to 100,000 miles. However, problems can happen much sooner. The best thing to do is look for the signs and symptoms an oxygen sensor is bad. The most obvious indicator is a lit Check Engine light; in this case, get an inspection or plug in a code reader to confirm. However, worsening fuel efficiency can also be telling, as it suggests your engine may be using too much gas in other words, the engine isn't getting the fuel-consumption feedback it needs. If you're still seeing problems with your oxygen sensors, check your vacuum hose first; it may simply require reconnection. Otherwise, check every sensor you've got. You can have two to as many as four. Some models have one on each exhaust manifold, while others can have one just after the exhaust system's catalytic converter. Need to replace your original Toyota Celica oxygen sensors? They're easy to change. Just unscrew old sensors and screw new ones into place. You can buy the genuine article from our online parts store. Order now and save!