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Diagnosing the Glowing Orange Demon on your Dash
By Matthew Wright, About.com
CHECK ENGINE. There's nothing fun about those two words. There's also not a lot of logic to be gathered from them. Check engine? Could they be a little more specific? Nope, they can't. That's because the Check Engine light comes to life if anything, and we do mean anything isn't 100% under the hood. This means that you could be staring at a major repair, or your gas cap could be too loose (no kidding).
Unfortunately, the majority of recurrent Check Engine episodes eventually lead to some professional repair time. The most common problems that trigger the light are emission control malfunctions. The emission control system is what your car uses to try to keep our air a little cleaner. To do this, it employs dozens of sensors, valves, flaps, heated wires and probably some fairy dust. Every car made in the last 20 years has at least one oxygen sensor (we saw a Toyota that had four of them recently), and they don't last forever. If they go, expect around $300 per sensor in replacement costs.
But don't throw your wallet in the street just yet. There are also plenty of little things that can make the Check Engine light come on, and many are easily corrected. Here are a few of the more commonly occurring issues:
Your gas cap isn't on tight enough.
You read that right, it might be your gas cap. Some cars measure how much pressure is building up inside your gas tank. It involves a series of mathematical algorithms that track your driving style and how much pressure is usually in the tank, then set off an alarm if it strays a certain percentage from the average. Whatever. All is means is that if you're gas cap isn't on tight, it thinks something is up and lights the orange dashboard candle, the Check Engine light. Tighten the gas cap and see what happens. It may take a week or more before the light goes out.
Your engine got wet where it didn't like it
Any electrical burp under the hood can cause one of your car's gazillion sensors to take a funny reading. When it does, you can expect to see the Check Engine light. We worked on a Ford truck once that triggered the Check Engine light every time it rained. After a lot of diagnosis, we found water that was dripping onto a spark plug wire, then running down the wire to the engine's head, causing an occasional short. Every time the water ran down the wire, the light came on. A few days later, it would turn off on its own. Be sure your engine doesn't have a wetness problem. More common than rain water getting in there is the overzealous owner who sprays his engine down at the high pressure car wash, shooting water into every crevice of the engine, thus lighting the light.
Your spark plug wires are bad
As your spark plug wires start to get old, they may develop tiny cracks which can let little bursts of electricity out. This electricity was supposed to be going to a spark plug, and since it didn't, the engine will misfire slightly, meaning one of the spark plugs didn't spark enough. Once again, this can cause the Check Engine light to come on. With your engine off, check your spark plug wires for tiny cracks or holes, especially around the ends of the wires. If they look shabby, you should replace them.
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Getting an accurate yellow “Check Engine” or “Service Engine Soon” light diagnosis is often frustrating and expensive. Fortunately, if you happen to be technically inclined and have the basic tools, it is likely that you can do the job yourself and avoid that expensive repair shop visit.
Designed to alert drivers to computer-monitored emissions problems, the “Check Engine” light is actually part of the vehicle’s emissions system. “Check Engine” lights became a standard equipment feature when automotive on-board computers proliferated in 1981. Federal law says that every new car sold in the United States must have a “Check Engine” light. But after more than two decades, “Check Engine” lights remain a mystery to many technicians and automotive do-it-yourselfers.
Here’s an ultra-simplified version of how the “Check Engine” light works. Vehicle computers use input signals from sensors to generate control signals for fuel, spark delivery, transmission shifting, and other functions. The car’s computer continuously monitors all input signals that could effect emissions. If any of the monitored signals move outside government-mandated limits, the computer turns on the “Check Engine” light.
The computer also determines if the problem meets the criteria for setting a code. However, rather than identifying a part or system that has failed, these codes refer to the part or system that is being affected by what has failed, making them more confusing than helpful.
Because this code system can confound even experienced technicians, it often results in unnecessary repairs. Oxygen sensors, for example, are extremely reliable, yet millions are needlessly replaced every year, largely because of the wide array of problems that cause the computer to set an oxygen sensor code.
Oxygen sensors examine the amount of oxygen in the exhaust gas leaving the engine. The sensor compares the oxygen inside the exhaust system to oxygen in the air outside the sensor. Rich exhaust has less oxygen; lean has more. The amount of oxygen in the exhaust is directly related to the fuel/air mixture entering the engine. A rich incoming fuel/air mix produces exhaust with less oxygen, while lean produces exhaust with more oxygen.
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What To Do If The "Check Engine" Light Goes On
These tips can help you determine whether your vehicle has a loose gas cap or serious engine problems.
You're driving along in your car or truck and suddenly a yellow light illuminates on your dash telling you to check or service your engine. If you're like most car owners, you have little idea about what that light is trying to tell you or exactly how you should react.
Call it the most misunderstood indicator on your dashboard, the "check engine" light can mean many different things, from a loose gas cap to a seriously misfiring engine.
"It doesn't mean you have to pull the car over to the side of the road and call a tow truck. It does mean you should get the car checked out as soon as possible," says Dave Cappert of the National Institute for Automotive Service Excellence, a Virginia-based organization that tests and certifies auto technicians.
Ignore the warning, and you could end up damaging expensive components. It also can be a sign that your car is getting poor fuel economy and emitting higher levels of pollutants.
WHAT THE LIGHT MEANS
The "check engine" light is part of your car's so-called onboard diagnostics (OBD) system. Since the 1980s, computers increasingly have controlled and monitored vehicle performance, regulating such variables as engine speed (RPM), fuel mixture, and ignition timing. In some cars, the computer also tells the automatic transmission when to shift.
When it finds a problem in the electronic-control system that it can't correct, the computer turns on a yellow warning indicator that's labeled "check engine," "service engine soon" or "check powertrain." Or the light may be nothing more than a picture of an engine, known as the International Check Engine Symbol, perhaps with the word "Check."
In addition to turning on the light, the computer stores a "trouble code" in its memory that identifies the source of the problem, such as a malfunctioning sensor or a misfiring engine. The code can be read with an electronic scan tool or a diagnostic computer, standard equipment in auto repair shops. There are also a number of relatively inexpensive code readers that are designed for do-it-yourselfers.
Manufacturers originally used the OBD system to help technicians pinpoint and troubleshoot malfunctions. But the systems now are required under federal laws governing automotive emissions. Although larger trucks have been exempt from the requirement, that quickly is changing.
"The 'check engine' light is reserved only for powertrain problems that could have an impact on the emissions systems," says John Van Gilder, General Motors' lead OBD development engineer.
Exactly what the OBD system looks for depends on the make, model and year. The original systems varied widely in their capabilities. Some did little more than check whether the various electronic sensors and actuators were hooked up and working.
That changed by 1996, when, under OBD II regulations, carmakers were required to install a much more sophisticated system that essentially acts like a built-in state emissions testing station. The computer monitors and adjusts dozens of components and processes.
For example, it continually samples exhaust emissions as they come out of the engine and again when they leave the catalytic converter, a device that removes carbon monoxide and hydrocarbon pollutants from the exhaust. The system also monitors your car's fuel system to ensure that gasoline vapors are not escaping into the atmosphere through a leak or even a loose or missing gas cap. In most cases, if a problem occurs, the computer will wait to see if it corrects itself before turning on the light. Modern OBD II systems are so thorough that state testing centers increasingly are checking for any stored trouble codes and foregoing the traditional tailpipe emissions test.
Some states are considering an advanced OBD system that would allow them to do away with emissions testing. If the "check engine" light comes on, the system automatically would send a remote signal to state officials, who would contact motorists who don't have the problem corrected within a reasonable amount of time. Privacy advocates are criticizing the idea as being too intrusive. Depending on the system, officials might be able to trace where the vehicle had been.
Proponents say the system would free motorists from the time and expense of having to undergo annual or biennial emission testing, and it would help ensure that emission-related problems are detected and fixed more quickly. Oregon expects to launch such a program on a voluntary basis in less than a year.
Remote diagnostics already can be found on GM vehicles equipped with the OnStar communications system. When the "check engine" light goes on, GM car owners can notify an OnStar representative, who can read the trouble code and provide advice.
If your "check engine" light illuminates don't react like one Connecticut motorist, who simply poured an extra quart of engine oil into her 2002 Toyota Corolla. Although extreme situations, such as low oil pressure or an overheating engine, might trigger a "check engine" light, your dashboard has other lights and gauges to warn you about those problems and probably a lot sooner.
The best advice is to read your owner's manual beforehand and learn the purpose of the "check engine" light and every other gauge and warning indicator on your dashboard. Periodically, you also should test the "check engine" light and other dashboard warning lights. Usually, you can do this by turning the key to the key-on/engine-off position. Consult the owner's manual for more information. Replace any bulbs that aren't working.
If the "check engine" light illuminates, it will either blink or remain constant, depending on the problem. Either way, you should have the vehicle checked by a mechanic, although a blinking light indicates a problem that needs immediate attention.
In late-model cars, a blinking light usually indicates an engine misfire so severe that unburned fuel is being dumped into the exhaust system, where it can quickly damage the catalytic converter, requiring an expensive repair. If that happens, you should reduce power and have the car or truck looked at as soon as possible. If the light is steady, the problem is not an emergency, but you should schedule an appointment as soon as possible. Today's automotive computers often try to compensate when there's a problem; so you may not notice deterioration in performance, even though your fuel mileage is suffering and your vehicle is emitting unacceptable levels of hydrocarbons and other pollutants.
"The customer is really, in a long run, potentially hurting their pocket book by leaving that light and ignoring it," says Jim Collins, a national training team leader for Ford Motor Company. In some extreme cases, the car's computer may reduce power for you, as it tries to limit the risk of damage.
If the check-engine light comes on, here are some tips on what you should do:
Look for a serious problem that requires immediate attention. Check your dashboard gauges and lights for indications of low oil pressure or overheating. These conditions mean you should pull over and shut off the engine as soon as you can find a safe place to do so.
Try tightening your gas cap. This often solves the problem. Keep in mind that it may take several trips before the light resets. Some vehicles have a separate indicator that warns of a loose gas cap before the condition sets off the "check engine" light.
Reduce speed and load. If the "check engine" light is blinking or you notice any serious performance problems, such as a loss of power, reduce your speed and try to reduce the load on the engine. For example, it would be a good idea to stop towing a trailer. Have the car checked as soon as possible to prevent expensive damage.
Contact OnStar, if available. If you have a 1997 or later General Motors vehicle equipped with OnStar and an active OnStar subscription, contact an advisor who can read the trouble code remotely and advise you about what to do.
Have the code read and the problem fixed. If you want to diagnose the malfunction yourself, you can buy a scan tool at most auto parts stores. Prices range from about $40 to several hundred, depending on the model and the features. The tools come with instructions on how to hook them up and decipher the codes. But unless you have a good knowledge of automotive diagnostics, you're probably better off taking the vehicle to a professional. Some automotive parts stores will read and interpret the code for you without charge. Unless there is an easy fix, they may simply refer you to a mechanic.
Don't go for a state emissions test. In a late-model car, an illuminated "check engine" light probably is a sure sign your car will fail the test. In some states, it's an automatic failure, even if the problem was nothing more than a loose gas cap. By the way, don't bother trying to fool the inspection station by disconnecting the battery or using any other method to erase the trouble code and turn off the "check engine" light. Your vehicle's computer will let the inspection station know that its codes have been erased, and you'll just have to go back again.
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