If my check engine light is on, does my car have to go to the dealer?

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Answered by: Roger Allen, An Expert in the Auto Repair - General Category
No. In today's market, there are various other ways to diagnose an engine fault code other than paying ridiculous dealership labor rates. A vehicle's check engine light may illuminate for several reasons ranging from smog/emission control errors to something as simple as a loose or missing fuel cap.

The Automotive Manufacturers install several circuits into the vehicle's diagnostic computer to aid the technician who is making repairs or maintenance to the vehicle. Each of these codes are assigned to a particular and specific component of the engine's operating system. Most modern vehicles have not just a fault code for a defective, or slower responding oxygen sensor, for instance but in fact up to four codes just for the oxygen sensors -- one for upstream, bank 1, one for upstream, bank tow, one for downstream, bank one and one for downstream, bank two.

Vehicles equipped this this degree of technology are actually among the easiest to diagnose. Many independent auto repair shops have the available testing equipment to read the fault codes. These diagnostic tools are proprietary to each manufacturer, however there are after-market tools available which will also read fault codes from many different vehicles.

Additionally, there are ways to self-diagnose the on-board diagnostic system in older cars as well, providing the diagnostic system has stored what is generally referred to as a "Hard Code." A hard code is a fault code, or trouble code that has been stored in the vehicles computer memory because the fault has reoccurred for more than a specified amount of key-cycles. It is not uncommon for the check engine light to come on if a glitch occurs, then extinguish and remain off. This just typically means that there is a sensor that has a short, and is probably on its way to failure, however the impending failure could be thousands of miles down the road.

If your vehicle is newer than model year 2000, it is most likely operating with a generation 2 or 3 diagnostic on-board computer. Many auto parts stores, such as Auto Zone or Pep-Boys will read these codes for you free, and often the result will reveal a fault that is covered under the Federal Emissions Warranty of 8 years/80,000 miles.

This could be of great benefit to you, the owner if the testing reveals an easy to install part that can simply be bought over the counter and installed in a matter of minutes, rather than making an appointment with the dealer, dropping the car off to sit in the parking lot all day and then being charged not only for the part, but also the labor to install the part and usually about $90 for the initial diagnostic that could be done free.

Older vehicles with a check engine light, for instance mid-1990's Fords may be diagnosed as simply as inserting a metallic object such as a paper clip into the diagnostic port under the hood, and counting the number of flashes of the check engine light on the dash of the vehicle. This flash coding will tell you exactly which circuit is giving a fault and turning on the check engine light.

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