How do you diagnose a Check Engine Light what does it mean and how do you reset it?

Answer 1

The Check Engine light is on because the computer has detected a problem with the emissions control system. Unless you fix whatever has caused the computer to set a fault code, it will come right back on. Depending on the model year of your vehicle and weather it is an OBD1 or OBD2 system, disconnecting the battery for a few minutes may reset the light, especially on an 1995 and older OBD1 system. Rarely will this work on a OBD2 system. On an OBD2 and some OBD1 systems, you need a scan tool to reset the light. Take it to any auto parts store and see if they will scan the system for you, free of charge. Depending on your state, they may accommodate you. The code they find will help to determine what is wrong. If you purchase the repair parts from them, they may reset the light after you make the repair. One thing to do before any of this is to check your gas cap. A loose gas cap will set the light. If you find that it was loose, tighten it, (3 clicks). The computer will turn the light off after a few driving cycles if that was the problem. == my 2 cents == 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.

== Answer == Before you do anything, go to Autozone and use their loan a tool program to chech out an OBD-II code reader. Follow the instructions on the box, or if you don't feel comfortable doing it yourself (it's really easy), have one of the store employees do it for you. My check engine light came on this past winter, and it turned out that one side of the engine was too lean. I remember the light came on when I started the explorer on a particularly cold day. Anyway, once you reset it, it probably won't come back on unless there is something wrong with some component.

== Answer == Take it to a garage and have them fix it is about the only way without "special tools". Otherwise: Pull 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. Therefore, another problem may exist. It is emission related. OR hook up a scanner that is capable of clearing codes, and hope that none are still active. Disconnecting the battery can create other headaches and will not likely solve your dilemma. Best bet is to contact the local snap-on dealer and have him refer you to a known good shop that specializes in this technology-he will know.

The " check engine light" is by far one of the most misunderstood technological advances by the public. This is an needed in-depth understanding for the public. It is a warning light that is illuminated when there is a problem affecting the EMISSION SYSTEM only. Emission system being the pollution control system. Don't get a hard on against it as it is a good thing once you understand it. One point that was brought up a 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 that about 7% 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 17 different computers) will run a series of self-tests. They will only run under certain criteria. And they can be vastly different from manufacturer to manufacturer. Some self-tests 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. 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 vastly, 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.

That is not entirely correct. An o2 sensor will not trigger a trouble code just because it has reached a preselected mileage. If the trouble code indicates a faulty o2 sensor it generally can be confirmed that it is faulty or something causing the trouble code such as a broken wire. To say that the check engine light is for emission system only is incorrect as well. The cars computers monitor a variety of things such as the air fuel mixture. The O2 sensors monitor the exhaust to ensure the proper mixture is accomplished. If you have an O2 sensor that has failed the computer will set the check engine light and not allow the system to go into "closed loop". This is when the computer will monitor a number of sensors like the "throttle position sensor" the "O2 sensors" and allow the computer to adjust the air fuel mixture. If the check engine light is on the engine will run a predetermined program and not make adjustments to provide the best performance and fuel economy. I think the best thing is to find out what trouble code has set the check engine light with a scan tool or have a tech do it for you. If it is an emission code that may not rest, such as a loose gas cap, then clear the code and see if it resets. If it resets, find out why and repair it.