With the data a functioning Pontiac oxygen sensor can provide your onboard computer, the best possible performance of your engine can be achieved. The oxygen sensor is the funny little probe that is sticking out of your exhaust pipe just below the exhaust manifold. The exact type of data the Pontiac oxygen sensor provides your onboard computer is the ratio of oxygen in the atmosphere as compared to what your engine is presently producing. This data is then used in the computation that determines the correct fuel to air ratio each cylinder will receive. It is true that the variation in oxygen levels is very minute, but that is how much precision is now put in the operating of the Pontiac engines. The oxygen sensor is made to last but since it is an electrical component, eventually if will fail. When this does occur, the check engine light will illuminate on the dashboard of the vehicle indicating there is a problem with one of the engine components. With a manual for your make and model of Pontiac, the owner of the vehicle can find the retrieval process for the codes from the computer. The codes are in numerical form, which are listed in the manual along with descriptions of what each code indicates. One of them is the code for a failing oxygen sensor. The only way to fix this problem is with the sensor being replaced. Before the oxygen sensor can be replaced on your Pontiac, the battery should be disconnected. This performs two functions. Not only will it be safe to work in the electrical components of the vehicle with no possibility of a shock or short occurring, but it will also clear all of the stored engine codes in the computer turning off the check engine light.