The only ways to reset the check engine light on a Dodge Neon are to use an onboard diagnostics tool or to disconnect the battery. Although disconnecting the battery resets the check engine light in most cases, most mechanics do not recommend this method for cars with anti-theft systems.
Dodge Neons made through the years 2000 to 2003 allow owners to figure out the code that the check engine light is indicating without using an OBD tool. This is done by putting the key into the ignition, turning it to the accessory position and then turning it off. After repeating this three times, the check engine light starts to flash. The number of times and sequence in which it flashes indicate the check engine code. For example, if the check engine light flashes twice, pauses and then flashes once more, this indicates code 21.
The OBD is used to give mechanics and vehicle owners an inside look as to what is wrong with a car. The amount of information provided by the vehicle's self-diagnostic system has greatly improved since it was introduced in the 1980s. Some of the first systems simply illuminated specific malfunction indicators if a problem was detected, but they did not give any kind of information as to the nature of the problem.