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Service engine light came on in 1999 Saturn SL2. Had oxygen sensor replaced already. Could it be bad gas or what else? Sandy

Answers from the Automotive Experts

Audra Fordin, Owner at Great Bear Auto Shop Hello Sandy, Depending on how much mileage you have on your car and what maintenance you have done in the past, will determine what your car needs. When your engine light is on, with a scanner, a code can be read allowing the tech to diagnosis what is needed to repair the trouble causing the light to come on. Mechanically yours, Audra

Diane Larson, Owner/Manager at Larson's Service Hi Sandy, Sorry you are having a problem with your Check Engine Light:) The Check Engine Light on your Vehicle can come on for lots of different reasons...It may or may not have to do with the same Code you had when the Oxygen Sensor was replaced.... Your computer is seeing a problem and tells you by turning that light on, however it can't tell you what is wrong. Depending on what Codes your Computer is giving, it could be one of many things, maybe something very simple.... Best to have the Computer Data read and the Vehicle Tested before replacing any parts....Sometimes the code can be deceiving - an Oxygen Sensor Code does not always mean a bad Oxygen Sensor, only that there is a problem with the Oxygen Sensor Circuit, which could be caused by many things:) Have a Fun Day! diane

Kristin Brocoff, Director of Corporate Communications at Hi Sandy, Those lights sure can be frustrating. Is it your check engine light or service light? Some makes and models have a reminder light that's triggered by mileage to remind you to have your oil chang. If it's the service/check engine light, it could be a lot of different things. The oxygen sensor that you replaced may not have actually been the one that was bad, or perhaps it triggered your car's computer to see a secondary problem. The best way to identify the true problem is to have it looked at by a qualified technician (I recommend an ASE Certified technician and shop). You can also get a home diagnosis with the CarMD product. The database has tens of thousands of fixes from technicians across the country, and can give you a spot-on description of the problem or problems, as well as the solution down to parts and labor in your area. Best of luck to you! Kristin Brocoff Corp.

Amy Mattinat, Owner and Author at Auto Craftsmen Ltd Sandy, We get asked a question at least once a day regarding the check engine light (also know as the “service engine soon light".) The most common question is, “Do I need to take my car to the shop ASAP when the check engine light goes on?” Our generic answer is: “When the check engine light comes on and your car has drivability problems, or if the check engine light starts flashing, you should drive it or tow it to the shop ASAP. You could do more damage to the vehicle if you continue driving it. Once the vehicle arrives, we will scan the computer to get a reading on what is wrong, or get a reading in which direction we should start looking for the problem. If there are no drivability problems then you can keep driving it and bring it in at your convenience.” The engine management/emission control systems in modern cars are /so sensitive/ that the light comes on due to hundreds of reasons.Sometimes it is as simple as the fuel filler cap being loose, driving the vehicle too hard under extreme conditions or using the wrong grade of fuel. The problem could also be in one of three areas: Engine Management, Emission Control, or Accessories. Although they are separate subsystems, the same computer controls them all. 1) /The Engine Management system/ is directly responsible for the fuel delivery and ignition/spark requirements of the engine. It uses a number of sensors to accomplish these tasks. The sensors provide input into the computer so that it can make adjustments for optimal performance. 2) /The Emission Control system/ is closely integrated with the engine management system and reduces exhaust and evaporative emissions, while maintaining optimal drivability. 3)/ Accessories/: On the newer automobiles, more components have been assigned to the engine management computer. They include the fuel pump, alternator, air conditioning compressor, and radiator cooling fan. All of these components are designed to operate within certain parameters that the computer monitors. When one of the components operates outside those assigned parameters, the computer recognizes this and your check engine light comes on to tell you something is wrong and needs to be fixed. Often, the computer is also programmed to switch into "failure mode," employing a pre-mapped strategy to compensate for the failure. This means you may not notice that the vehicle is driving any differently than normal, but your car is working overtime to do this for you. It may also create a noticeable drivability problem, so if the bright yellow light on your dash is not enough motivation, the car driving badly will get you into the shop ASAP. This being said, after having a sensor replaced it is not uncommon for that darn light to come on again. It is annoying for the customer and annoying for the shop. After rescanning the computer, the shop may recommend a different sensor be replaced. There are a number of them, and it’s not uncommon to have more then one fail at the same time. So, my long winded answer to your question is: take your car back to the shop that replaced your oxygen sensor, and have them re-scan your computer to see why the light came on again. Sincerely, Amy Mattinat Auto Craftsmen Ltd Automotive Experts LLC

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