How To Clear Obd Ii Trouble Codes

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Your check engine light typically comes on when there is a problem with your emission control system or another computer-controlled system in your vehicle. The light generates a code that can help you narrow down the problem so you can get it fixed. You may also need to manually reset the light after making repairs if the code doesn't clear automatically. The best way to reset a check engine light is to use a code scanner. However, if your vehicle was manufactured before 1996, you can simply disconnect the battery to reset the light.

1
Buy or borrow an OBD-II code scanner. "OBD" stands for "On-Board Diagnostics" and OBD-II scanners are suitable for all vehicles made after 1996. Purchasing a code scanner can be costly, so it's better to borrow one unless you plan on using it frequently. Some auto parts stores loan out scanners to patrons, or you could borrow one from a friend or family member.^[1]
- Note that vehicles made before the 1990s may not have an OBD port under the dash. If they do, it may be an OBD-I port rather than an OBD-II port, so you may need a different scanner.
2

Plug the scanner into the port under the steering column. Modern vehicles have ports specifically designed for OBD scanners. Look underneath the steering column to find the port, then connect the cord attached to the scanner to the port. Refer to your vehicle's manual if you cannot find the port.^[2]
3
Turn the key to the "on" position and press the "read" button on the scanner. Put your key in the ignition and switch the vehicle to "on." Do not start the vehicle. Once the lights on the dash come on, turn off all the vehicle's accessories, like the radio. Then, press the "read" button on the scanner to access the check engine light code.^[3]
- The code will be a series of letters and numbers. Record all of the codes so you can figure out what they represent and make the necessary repairs to your vehicle.
- Some scanners will define or explain the codes while others will not. If you don't get a definition, look up the code in the owner's manual or online.
4

Press the "erase/clear" button on your scanner, then turn off the key and disconnect it. Clearing any codes present will turn off your check engine light temporarily. After pressing "erase/clear" and waiting until you see a "no codes" message, you can turn off your vehicle and disconnect the scanner. However, erasing the codes does not fix the problem. If your check engine light comes on, it's best to take your vehicle to a mechanic to get it professionally diagnosed and repaired.^[4]

Warning: Once the OBD system resets (which occurs after a few drive cycles or a certain number of miles, depending on the vehicle), the light will come back on if the problem has not been fixed.

1

Remove the negative cable from the vehicle's battery. Pop the hood and locate the battery. Use a wrench to remove the negative cable, which is usually covered with a black cap and marked with a minus sign, from the terminal.^[5]

Warning: Erasing codes by disconnecting your vehicle's battery can also clear out the memory for your radio and other onboard components.
2

Drain any remaining electricity from the capacitor. Press and hold the horn for 30 seconds or try to switch on the vehicle's lights. Neither the horn nor the lights will work since there's no power running to them, but attempting to do so will use up any electricity in the capacitor.^[6]
3

Wait 15 minutes and reconnect your battery. Leaving the battery disconnected for about 15 minutes will ensure the vehicle systems will completely reset when you reconnect the battery. Secure the negative cable back to the terminal and cover it with the cap (if applicable). Disconnecting the battery will clear the error codes and reset the check engine light.^[7]

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Reputable auto shops will not reset a check engine light without fixing the problem that caused the light to come on.
Consult a mechanic or repair shop if you need help resetting a check engine light or deciphering error codes.

The emissions monitors in your vehicle will register being reset, so you will not pass emissions if you bring in a car immediately after resetting the codes. Drive your car for at least 200 miles (320 km) before bringing it in for an emissions test.
Use caution when disconnecting and reconnecting the battery.

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Sometimes your check engine light won't turn off even after you've fixed the problem with your vehicle. When that happens, you'll need to manually reset the light. One option is to turn the ignition on and off 3 times in a row. Then, drive your vehicle around and check to see if the light goes off. If that doesn't work, turn off your car, pop the hood, and disconnect the positive and negative cables from the battery. Press on the horn for 30 seconds to drain any remaining electricity, then wait 15 minutes before reconnecting the battery cables. Disconnecting the battery like this may reset your car's electrical system and erase the error code that's causing the check engine light to stay on. If all else fails, purchase an OBD code scanner and plug it into the OBD port on your vehicle, which should be located under the steering column. Turn on the scanner and wait for it to scan your vehicle for error codes. When it's finished, you can erase the error codes that appear on the scanner, which will turn your check engine light off. To learn how to reset a check engine light with a code scanner, read on!

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