How to Reset the Check Engine Light on a 1990 300E

1. Open the plastic battery cover to expose the battery. Identify the negative terminal, which is marked with a minus symbol, and remove the attached cable using a crescent wrench.
2. Wait at least 15 minutes, then reverse the steps to reinstall the cable. Confirm that the nut is tight enough to hold the cable in place and ensure a strong electrical connection.
3. Start the engine and allow the Mercedes to idle for 5 minutes before driving. This gives the computer system time to recalibrate and ensures the engine will run smoothly when driven. Keep an eye on the dash to see if the light returns. If it does, then further repairs are in order to solve the underlying problem.