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Mechanic’s confession, about that 'check engine' light.

July 20, 2011 - Larry DeHays
Everyone has had that amber CHECK ENGINE light come on. You check the oil and water, and nothing seems to be wrong. What now? Here’s the scoop. That light has nothing to do with your oil or water, or practically anything else you can personally check on your car. It simply means that your emissions are out of specifications. In other words, you are polluting the atmosphere. It has nothing to do with how well your car is running, only that it is polluting. It should be “CHECK COMPUTER” rather than “CHECK ENGINE,” but what’s in a name. A polluting car by any other name smells as bad. (Apologies to the Bard). The reason your car is polluting could be something that also affects the way it runs, (like a fouled spark plug) or it could be as simple as leaving the gas cap too loose after refueling, which lets gas fumes escape. These trigger the CHECK ENGINE light. Your car’s computer controlled engine management system is very sophisticated compared to the old days. It now checks various sensors all over the car for things like incoming air temperature and air volume, oxygen content in the exhaust, air pressure in the fuel tank, and many other things concerning emissions that may or may not be detectable by the driver. A specialized scanner, plugged into the computer system gives a “trouble code” which narrows the diagnostic effort to a specific system of the car. Lately, automotive parts stores and other places have been using scanners in their parking lots to tell their customers what the “trouble codes” are, and people are buying parts that they think might be the cause. Caution should be used here, because an oxygen sensor code might not mean the oxygen sensor is faulty. It could mean that there is a fault causing the oxygen content to be off, and the sensor is actually correct. Replacing the sensor will not correct the fault. The mechanic’s confession here is that we hope you will bring your car to us when the light comes on for a professional diagnosis, and we wish you had a better understanding of the complexities involved. Many times one sensor may cause the light, and the problem is repaired. Then another sensor causes the same light to come on again, and you get angry with us because the light is “still” on. It is one light with multiple triggers, and we spend a lot of time trying to explain that. One final note, there is a product advertised now directly to the consumer, to plug into your own car so that you will know “exactly what is wrong and what it will cost” to repair. Impossible. Beware of scams. Any thoughts on the subject?


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