Why does a check engine light come on?

The check engine light comes on and stays on when a problem is detected by the self diagnosis system of your vehicle. Generally, a check engine light is lit when there is a problem in the emissions or somthing that is affecting the effectiveness of the emissions. your engine computer found a problem with a sensor or how the engine overall is running Youn need to goto a mechanic shop and have them use a scanner to diagnose the code then tell you what parts and labor it is to repair The " check engine light" is by far one of the most misunderstood technological advances It is a warning light that is illuminated when there is a problem affecting the EMISSIONS of the vehicle.. Don't let it bother you as it is a good thing once you understand it. One point that was brought up a recent meeting of technicians was that the amount of hydrocarbons is greater when the gas cap is left off than when the engine is running. Hydrocarbons are part of pollution emitted as gasoline evaporates. Going a step farther, one facet of the emission system is the "Evaporative" portion. This is when the fumes from the gasoline are leaking from the system into the outside air. This is one part of the emission system that can trigger a check engine light. I would say a small percentage of the vehicles that have a check engine light are the result of a loose or inadequate gas cap. But understand that many scenarios are possible with the "check engine light" The vehicle's powertrain computer (note that some vehicles have multiple computers aside from the powertain computer) will run a series of self-tests. They will only run under certain criteria. And they are different from manufacturer to manufacturer. Some self-tests or �monitors� are not run until preceding ones have run successfully. So if there is a problem in one particular area that is preventing another self test from running, you can have a situation where one problem is fixed, but another still exists. If you fix a problem and drive the car through a drive cycle that sets the monitor (or self test) the light will go off as it passes that criteria that triggered it in the first place. There are many different sources for the light to come on. Anything that caused combustion to fail, commonly called a misfire will set the light. Various sensors such as oxygen sensors that evaluate the exhaust before and after the gases are burned in the converter. Transmission codes may set the check engine light to appear. If the car is running okay, get it fixed in a reasonable amount of time such as within the month. It will probably save you fuel if you do. However if the Check engine light is flashing, you should be driving it as damage is being done to the converter. Some emission components are covered beyond the standard warranty. The converter for example is covered up to 80,000 miles by the manufacturer. After 1996, the auto industry went to a idea called OBD II (on board diagnostics). This was to get all the manufacturers onto a similar plane for troubleshooting and powertrain control. While they still differ, many corrections and adaptations were made for technicians to better fix the check engine light problems. Prior to this there were so many different and poor troubleshooting data from a check engine light problem that resolving the problem was much more difficult. Many early warning light of this nature were set to illuminate based on mileage. An Oxygen sensor was one of the things that were meant to be replaced when that mileage was hit. This is much like many current "Change oil lights� that are set based on a pre-set mileage. To start testing for the check engine light, you�ll need to find the codes from the computer, match the code to the troubleshooting procedure, follow the procedure to find the source. Repair the source, light will go out if that was the only problem. There are "monitors" or self tests the computer runs the car through a drive cycle, if a problem occurs, it may not run all of the self tests until that problem is taken care. There are self-tests for the oxygen sensor circuit, egr system, evaporative system to name a few. Therefore, another problem may exist. It is emission related. OR hook up a scanner that is capable of clearing codes, and hope that it won�t come back on. But don�t bet on it.. 1996 Ford Contour is sometime caused by a misfire on startup. The error will clear itself after 3 complet warm-up cycles not restarts. A flashing check engine light is an indication of a severe misfire. You need immediate service. go to autozone they will hook up an OBD II scanner to your computer and explain the codes to you. There are pages and pages and items that can cause a check engine light. You need to have it checked for codes with a scan tool. After repair light can be shut off with scan tool. The check engine light comes on at start up for a bulb check. If it stays on with the engine running the computer has detected a malfunction. You need to have it checked for codes. Sometimes it comes on when you have to replace your air filter due to it being dirty. It will also come on when the gas cap is not tightened or needs to be replaced. -------------- Not all systems are able to be read by your local auto parts store. For '95 and later cars, OBD I is used and can NOT be read by autozone or advanced auto. A simple paper clip can be used to jump 2 ports on the diagnostic port and have the Engine light flash a certain sequence. This will then tell you the code to refer to for troubleshooting. Have vehicle scanned to determine problem ---------------- There could be hundreds of reasons ranging from issues with the engine control computer to a clogged exhaust. To find the answer plug a tester into the OBDII port inside the car. You'll find the port under the dash to the right of the steering wheel column. Many auto supply stores will loan you the test unit at no cost or will run the test for you. The tester will either give you a numerical code (which you then have to look up) or will tell you what the problem is on the screen. Once you've fixed the issue you can use the tester again to clear the code and the light will go off. A "Blinking" light typically means that something SEROUS has been detected. Use a code scanner to detect the problem. You will have to get a engine scanner and scan the engine. And it will give you the trouble code or codes, and then fix the problem. The computor is seeing a problem

in the engine system or transmission system. Need to repair. go to auto zone and have them check it for you. its free This could possibly be the engine management light if so it means the system has detected a fault. The car needs to be connected to diagnostic equipment for fault diagnosis and the light to be re set.