The check engine light (CEL for short) is triggered when one or more of the many sensors on the vehicle detects a not-normalreading,

There are 2 basic steps to determining the cause of the CEL coming on:

1. Have the codes read - many places offer to read the engine codes for free. Autozone even provides a printout of the codes, and a short description of common causes
2. Research those codes! Find out the true cause and reason for the not-normal reading. It is not often that the sensor itself is bad and requires replacing.

   There are countless sources of information on engine DTC (diagnostic trouble codes) on the internet - including WikiAnswers!

Real-life examples:

• DTC code P0402 on 98 Tracer - replaced the EGR valve, light came back. Made my daughter live with it for 2 years. Yesterday I had a few minutes while waiting for the oil to drain and poked around the engine - found a small 2" piece of rubber hose that had softened and collapsed right where the PCV connects. A free piece of hose from Autozone and the light cleared after a few drive cycles!
• Major auto parts chain told me my TSP (Throttle position sensor) was bad due to the CEL being lit up (might have been a P1120 DTC). $40 and 10 minutes to replace - ((_#*&$ light came right back. A few days ago, after doing some reading, I bought a $4 can of throttle body spray cleaner - used 1/2 the can on my 98 Sable - voila! CEL is gone again!

Pay attention to those check engine lights - they're there for a reason. And with the internet today, you can readily find the information to keep your car healthy, and even save some $$ in the process.

(end of editorial rant,... and no more acronyms!)

NOTE:This light has 2 other names it is referred to:

• Service Engine Soon - SES
• Malfunction Indicator Lamp - MIL

AnswerYour owner's manual will tell you. It more than likely means it is time to change the oil. It can also mean there is a problem with the emissions controls, depending on what term Ford uses. AnswerIf your car is a year 96 or newer, this usually means there is a problem with your emissions system. This light will also detect a problem with your transmission, as some transmission problems will in some way affect gas efficiency, therefore affecting emissions (i.e. problems with overdrive performance) I know, I'm having this problem now. I have a 97 Mercury Sable. AnswerCHECK FOR VACUUM LEAKS! Everytime my engine light comes on, I get it checked at Autozone and they always tell me its a vacuum leak. I then have to manually search for a "sssss" sound on every vacuum line and replace the hose. The first time this happened, I found a huge hole in the hose next to my PCV valve, causing that to clog. I would recommend checking there first.

You need to have it scanned,most of smaller repair shops will do it a reasonable price,and give you the trouble code.

Check engine light staying onYou need to go to a reputable shop and have them test the vehicle. They will use a scan tool to check for codes, then they will have an idea what system is causing the light to come on.

Just finding out the code doesn't tell what's wrong, so it may not be worth trying to buy a cheap "code reader". Find a shop you trust and take the vehicle to a professional.

AnswerThe scanner / code readers are very inexpensive now - I've seen them as low as $30. Autozone & Harbor Freight are just 2 places to look.

BEWARE - the parts stores are very happy to tell you the DTC code (Diagnostic trouble code), and then encourage you to buy the cited part.

For example, a P0171 or P0174 indicate an oxygen sensor issue - will buying and replacing the O2 sensor FIX the problem? NOT AT ALL LIKELY. Don't just blindly buy the part - been there, done that.

Get the codes read - then research them on the net or talk to a reliable mechanic.

Its the emissions light. On my mercury sable when I get bad gasoline the light tends to go on. Usually if I run the car almost empty and then fill up again it goes out. If not try disconecting the battery.

It could be one, more, or MANY things. That's why it is suggested that you take it to your dealer if it is still under warranty. You can take it to AutoZone and have your "Codes" (what causes the Check Engine Light or "SES" Service engine soon light) read.

It will usually tell you what caused the SES and it should be fairly simple to fix, such as a malfunctioning O2 Sensor.

Some things however can be very complex and it is recommended an AST Certified Mechanic takes a look at the vehicle.

most likely a severe engine misfire. you need to have it checked for codes

AnswerIt simply means that the engines computer is picking up a a problem from one of the sensors on the vehicles All of the sensors work together and feed their information to the Engines Computer (or ECU). The main reason for all of these sensors is to accomplish maximun fuel economy while buring as clean as possible thus keeping pollution and emissions to a minimal. AnswerThe light is on because the computer has detected a problem with the emissions system. This may be nothing more than a loose gas cap, or as serious as a bad catalytic converter. Have the computer scanned for fault codes. This will help to find the problem. After the problem is corrected the light can be reset with an OBD2 scan tool. AnswerPull 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 test the computer runs the car through, 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. See "Related Questions" below for moreAnswer

Open and read your owner's manual. There you will find the answer to your question. But I will tell you. The computer has detected a fault with the emissions system.

Answer

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.

The " check engine light" is by far one of the most misunderstood technological advances by the public. I am sure I will revise this as time goes on, as it is an in-depth understanding for the public. It is a warning light that is illuminated when there is a problem with 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.

AnswerIt will be impossible to give you any better than a broad answer here, because there are literally hundreds of possibilities as to why a check engine light(CEL) comes on. The system would have to be scanned to retrieve whatever fail codes there are. Then we would use a manual (that is literally 3 inches thick)that contains flow charts with pinpoint tests, using a voltmeter, to hand diagnose, and find out what is wrong. This process can take a few minutes, it may take a couple of hours, depending on what is actually wrong.

Now here is the "why" of a CEL: What is actually turning on the CEL is the Powertrain Control Module(PCM), commonly known as the engine control computer. Inside of a PCM there are actually two separate systems. One is control, the other system is diagnostics. PCM diagnostics acts as "big brother," constantly looking over the shoulder of the control side of the PCM. Diagnostics is constantly monitering systems to see if the expected voltages and values are present. For example: If the PCM diagnostics knows that it has been so many minutes since the engine was first started, then the engine temperature should be around 195 degrees. In our senerio, if the engine is still 160 degrees, it sees a problem, and sets the CEL. The technician has to use pinpoint diagnostics to see if we have a stuck thermostat, if the Engine Coolant Temp(ECT) sensor if sending a false signal, if the wiring between the ECT and the PCM is bad, or if the PCM is faulty and interpreting the signal received from the ECT incorrectly. But the PCM is not capable of monitering everything all at once, so it basically goes down a checklist, over and over again, as you are driving down the road. Sometimes a problem can come and go intermittantly, at the right times so as to avoid detection by the PCM. That is why sometimes a CEL doesn't always come on everytime there is a problem. Sometimes you can unplug a sensor even while the car is running, and it takes a while for the CEL to come on, just because the PCM diagnostics hasen't gotten back around to looking at that area yet.

Our senerio only talked about one area that a PCM moniters. There are dozens of sub-systems that the PCM looks at, and dozens of possible failures within each of those sub-systems, that could cause a CEL.

Most often the cause of this light staying on is a bad EGR valve or a bad O2 sensor.

Y-THINK-Y

Answeryou might want to check your gas cap if it is loose it can trigger your check engine light

another questionI have been looking for a turn signal switch and can't find one.

To replace it you should just be able to take off the cover around thesteering column and snap it in where the old one was. I would be able Tobe more detailed if I could find a replacement.