Engine check light comes on. OnStar diagnoses fuel system problem. Dealerhip cannot find the problem even though the light was on when they checked it. It has been there three times.

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Bad coil, bad plug, bad wire.

Yes, the economy fuel saving light will not come on because you are not saving fuel while driving with the check engine light on, you are WASTING fuel.

The reason the check engine light is on is to inform you that there is a malfunction in your engine control system. You need to get the problem properly diagnosed and repaired.

Please also review the following article:Why Is My Engine Light On?

All modern vehicles are equipped with an onboard computer diagnostic system (OBDII) that constantly monitors your vehicle's major operating systems and most importantly the power-train (engine and transmission). The main purpose of monitoring these systems is to insure that the vehicle is operating at top efficiency with the lowest possible emissions. As fuel economy and emission control has become increasingly important and complex, your vehicle's electronics systems need to constantly adjust and fine-tune various parameters according to driving conditions (such as vehicle load, temperature, and air/fuel mix to name just a few). When the computer reads that any of these parameters do not fall within the acceptable range for operating the vehicle, your CHECK ENGINE LIGHT is lit to warn you that you may have a serious problem and to take your vehicle to a certified technician - such as your local AAMCO technician - to check the faults and restore it to manufacturer's specifications.


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. On some cars, a yellow "check engine" means investigate the problem, while a red "check engine" means stop right now.
- 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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you have a small leak in your evaporative emission system.the first thing to check is your gas cap.make sure to tighten it until it clicks three times.have the code cleared and see if the code comes back.

It sounds to me like the throttle position sensor is bad. The fuel injection cleaner might not help this case. Since your car newer than a 1996,you will have a computer system known as an OBD2. This diagnoses anything wrong with the car and will set the check engine light on whenever there is something wrong with the system. I suggest hooking an OBD2 scanner up to it and see what the code reads. Even though it may be off now,the computer should store the code for a while. Also if they hook up more complex scanner to it,they can see what is going on with the car as they drive it.

The "check engine" light is part of your car's so-called onboard diagnostics (OBD) system.

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. On some cars, a yellow "check engine" means investigate the problem, while a red "check engine" means stop right now.
• 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.

Hope helps.

Have you scanned for any trouble codes?... do you get a 'CHECK ENGINE' light when this happens?Whenever the 'CHECK ENGINE' light comes on, the ECU (Engine Control Unit) sets a Diagnostic Trouble Code (DTC). These codes identify the particular engine management system which caused the light to come on. You'll need to use/find an OBDII (On-Board Diagnostic) Scanner to retrieve any code(s) which have been stored in the ECU computer. Afterward, we might be able to help you DIAGNOSE the problem and perhaps eventually fix it. If you suspect the fuel pump, hook up a pressure gauge to the fuel delivery hose/line - you should have approximately 50 psi to the injectors. The problem could also be caused by wiring/connectors at the fuel pump or inside the fuel tank at the fuel pump.

Many possible causes for this. Do you have a "Check Engine" light? Whenever the 'CHECK ENGINE' light comes on, the ECU (Engine Control Unit) sets a Diagnostic Trouble Code (DTC). These codes identify the particular engine management system which caused the light to come on.
You'll need to use/find an OBDII (On-Board Diagnostic) Scanner to retrieve any code which have been stored in the ECU computer. Afterward, we might be able to help you DIAGNOSE the problem and perhaps eventually fix the problem.
Soot/Carbon buildup on plugs can be caused by many things, like leaky intake valve seals, excessive crankcase emissions being sent back into the intake air hose, leaky fuel injectors causing an excessively "RICH' fuel mixture, excessive fuel pressure from the fuel pump, faulty fuel pressure regulator, worn/faulty PCV, a faulty O2 sensor (upstream) or even a defective ECU.

the check engine light comes on whenever one or more of about 200 faults occur in the electronic engine or emmision controls, the only way to determine which system is causeing the problem is to have the system computer tested for the trouble code(s) that is stored when the light is turned on by the computer, which is known as the PCM