Reset Check Engine Light Tips

OBD

On-board diagnostics (OBD) were designed to integrate computers into engines in order to communicate and aid in diagnosing mechanical and technical repairs. However, the first OBD systems were non-standardized, and every car seemed to require different attachments and computer equipment to ascertain the trouble codes. Some required no equipment and could be decoded by counting blinking dash lights, but the codes were general and diagnoses didn't seem to be any easier with the computerized system.

On a vehicle made prior to the implementation of OBD II in 1996, the easiest way--and cheapest--way to reset a check engine light was to unhook for the battery of the vehicle to erase the trouble code.

OBD II

OBD II standardized computer equipment to diagnose trouble codes. Every car now has the exact same diagnostic link connector to hook a scan tool or code reader up to in order to read the trouble code and/or erase the code.

As technology advances, more and more electrical and computerized gadgetry is added to cars. Unplugging the battery is no longer the best option, and, in fact, often advised against by the manufacturers. Cars nowadays learn how you drive them and store this data, and cars with alarm systems and theft-deterrent radios can all be affected by unplugging the battery.

Since the cars made in 1996 and later all take the same computer equipment to read and erase codes, the best way to reset a check engine light is with a scan tool or a code reader/eraser. Most parts stores sell them, and will often even offer to read and erase the code for you.

Resetting the Code

Understand that the MIL is there for a reason. Resetting the light without diagnosing the problem is counterproductive. Some 'soft' code readings, like a small emissions leak, could be caused by a loose gas cap. Once tightened and the MIL reset, the problem will be solved. After a few cycles, the computer will register that the problem was solved and shut the light off on its own. But 'hard' codes will not only not reset, but you can also damage other components by trying to ignore the problem and continue to operate the vehicle.

Because computers in cars are self-learning, they have to go through several driving cycles to restore the data and fix the IM monitor that triggered the MIL. And if a repair is made to the vehicle to fix the cause of the check engine light lighting up, the vehicle will register that the problem was fixed and eventually reset the light by itself.