How to Reset a GM Check Engine Light

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The dreaded "Check Engine" light on your dash is illuminated and taunting you. You fear the worst. You can't afford a big repair bill, or worse, being without your car for an extended period. Thankfully, the light can come on for a variety of reasons, and not all of them involve the imminent collapse of your engine. A loose fuel cap hastily screwed in at your last pit stop will trigger it, so take a deep breath and figure out first what the problem is before lapsing into full-on panic mode.

Things You'll Need

  • OBD2 scanner
  • Error code chart

Instructions

  • Determine the type of error your car is reporting. A "Check Engine" or "Service Engine" light will illuminate in two ways. If the problem is minor, the light will come on, then go off again after a short drive. If the problem is more immediate or if the same minor problem has been detected by the car's computer repeatedly, the light will remain on until the error code is cleared.

  • Buy an OBD2 scanner. OBD stands for On Board Diagnostic. They can be expensive for the deluxe models, but careful searching should help you find a unit for about $150, and the device interface is standard for all U.S. vehicles from 1996 on. You'll usually find the input connection under the dash on the driver's side of your car.

  • Follow the manufacturer's instructions for scanning with the device and check the results against the provided error code charts, or look up make-specific error codes online.

  • Use your scanner to clear the error code from the car's computer after you've made the repair. To test for a false positive, clear the error code without making the repair. This will turn off the light and put the computer into a diagnostic mode for a specified distance, usually about 60 miles. If the light returns, there is a persistent problem that needs attention.

  • Try alternatives first if buying a scanner is not an option. On some makes and models, disconnecting the positive battery terminal for several minutes causes a computer reset, and the error code will clear. Also, most large auto parts stores will scan your car for a very reasonable fee and clear the code to test for a false positive.

Tips & Warnings

  • Use caution when dealing with battery terminals. When the positive terminal is removed, wrap it in cloth and fasten it with a rubber band to prevent unwanted contact with the negative post.

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