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When the Check Engine Soon Light comes on , your first instinct is to pull over and check out the situation. This is not necessary. This is the vehicles way of letting you know at its earliest stage that an error has occurred. No need to panic. If you have been driving with that all annoying light on, remember this : Your gas mileage will improve if the necessary repairs are made.


The First Thing To Do

The first thing to do when your "Check Engine Soon" light comes on is to determine the immediate cause. Consider if the vehicle is still performing as usual or if a loss of performance is noticeable. Generally a constant illuminated light without loss of performance points to an emissions related issue( this won't leave you stranded). When the light flashes, this indicates a serious engine failure condition and will require immediate attention. You may wish to take your vehicle to a local shop and have Computer Diagnostics performed. Usually costs under $100.00.

Generally all vehicles from 1996 and up have an OBD II computer. The Major problem when it comes to OBD II is that you can no longer acquire the trouble codes by counting the flashes of the Check Engine light like you could on earlier OBD I vehicles. You can take your car into a local high-tech service shop, where the minimum charge for computer diagnostics and engine diagnostics might cost you somewhere into three digits. Or you may want to learn about OBD II systems. in order to do so you will need an OBD II scan tool. I have already done the research for you and located several different scan tools for you to choose from. If you already have the code and need to know what it means check out our complete list of OBD II Codes Here.

Your vehicle has a computer which monitors operation of the fuel, ignition, and emission control systems.

This system is called OBD II (On-Board Diagnostics-Second Generation) and is intended to assure that emissions are at acceptable levels for the life of the vehicle, helping to produce a cleaner environment. The check engine light comes on to indicate that there is a problem and service is required. Malfunctions often will be indicated by the system before any problem is apparent. This may prevent more serious damage to your vehicle. This system is also designed to assist your service technician in correctly diagnosing any malfunction.

Caution! If the vehicle is continually driven with this light on, after a while, the emission controls might not work as well, the vehicle's fuel economy might not be as good, and the engine might not run as smoothly. This could lead to costly repairs that might not be covered by the vehicle warranty.

Caution! Modifications made to the engine, transaxle, exhaust, intake, or fuel system of your vehicle or the replacement of the original tires with other than those of the same Tire Performance Criteria (TPC) can affect your vehicle's emission controls and may cause this light to come on. Modifications to these systems could lead to costly repairs not covered by your warranty. This may also result in a failure to pass a required Emission Inspection/Maintenance test. See Accessories and Modifications .

This light should come on, as a check to show you it is working, when the ignition is on and the engine is not running. If the light does not come on, have it repaired. This light will also come on during a malfunction in one of two ways:

    •  Light Flashing  -- A misfire condition has been detected. A misfire increases vehicle emissions and may damage the emission control system on your vehicle. Diagnosis and service may be required.
    •  Light On Steady  -- An emission control system malfunction has been detected on your vehicle. Diagnosis and service may be required.

If the Light is Flashing

The following may prevent more serious damage to your vehicle:

    •  Reducing vehicle speed
    •  Avoiding hard accelerations
    •  Avoiding steep uphill grades
    •  If you are towing a trailer, reduce the amount of cargo being hauled as soon as it is possible

If the light stops flashing and remains on steady, see "If the Light Is On Steady" following.

If the light continues to flash, when it is safe to do so, stop the vehicle. Find a safe place to park your vehicle. Turn the key off, wait at least 10 seconds and restart the engine. If the light remains on steady, see "If the Light Is On Steady" following. If the light is still flashing, follow the previous steps, and see your dealer for service as soon as possible.

If the Light Is On Steady

You may be able to correct the emission system malfunction by considering the following:

Did you recently put fuel into your vehicle?

If so, reinstall the fuel cap, making sure to fully install the cap. See Filling the Tank . The diagnostic system can determine if the fuel cap has been left off or improperly installed. A loose or missing fuel cap will allow fuel to evaporate into the atmosphere. A few driving trips with the cap properly installed should turn the light off.

Did you just drive through a deep puddle of water?

If so, your electrical system may be wet. The condition will usually be corrected when the electrical system dries out. A few driving trips should turn the light off.

Have you recently changed brands of fuel?

If so, be sure to fuel your vehicle with quality fuel. See Gasoline Octane . Poor fuel quality will cause your engine not to run as efficiently as designed. You may notice this as stalling after start-up, stalling when you put the vehicle into gear, misfiring, hesitation on acceleration, or stumbling on acceleration. (These conditions may go away once the engine is warmed up.) This will be detected by the system and cause the light to turn on.

If you experience one or more of these conditions, change the fuel brand you use. It will require at least one full tank of the proper fuel to turn the light off.

If none of the above steps have made the light turn off, your dealer can check the vehicle. Your dealer has the proper test equipment and diagnostic tools to fix any mechanical or electrical problems that may have developed.

Emissions Inspection and Maintenance Programs

Some state/provincial and local governments have or may begin programs to inspect the emission control equipment on your vehicle. Failure to pass this inspection could prevent you from getting a vehicle registration.

Here are some things you need to know to help your vehicle pass an inspection:

Your vehicle will not pass this inspection if the check engine light is on or not working properly.

Your vehicle will not pass this inspection if the OBD (on-board diagnostic) system determines that critical emission control systems have not been completely diagnosed by the system. The vehicle would be considered not ready for inspection. This can happen if you have recently replaced your battery or if your battery has run down. The diagnostic system is designed to evaluate critical emission control systems during normal driving. This may take several days of routine driving. If you have done this and your vehicle still does not pass the inspection for lack of OBD system readiness, your dealer can prepare the vehicle for inspection.

OBD II scan tools connect to the vehicle's computer through a connector under the dash by the steering wheel.

Check Engine Light

Need specific information ? Check out Ask FreeAutoMechanic Experts Questions.

Sample Answer below :

VW Jetta GLI/VR6, 2003

The error code, "P3081" has been identified from a recent diagnostic and I was wondering if you could be so kind as to help me interpret what this code is and how, perhaps, to remedy this problem..if any...

"19537 4C51 P3081 Engine temperature too low"

That DTC is indicative of a missing thermostat, a stuck open thermostat, or a cooling system with 100% antifreeze. It is NOT associated with a defective ECT G62.

When the coolant temperature is too low, that does not necessarily mean a sensor failure. Sounds like the sensor is telling you the truth.
Watch the temperature on the scan tool as the engine warms up. Look for things that keep it from warming up. Things like radiator fans on all the time, straight anti-freeze, stuck open thermostat and so on. That is what it means. It means a system problem, not necessarily a component failure.

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