1. Make sure that the issue causing the CEL to illuminate has been resolved or repaired. The check engine light can indicate various issues, such as emission system faults, sensor malfunctions, or engine misfires.
2. Once the problem is resolved, you will need a scan tool compatible with OBD-II (On-Board Diagnostics) systems to clear the trouble codes and reset the CEL.
3. Locate the OBD-II port in your vehicle. In the 1999 Mercedes-Benz 500 SL, it is usually found under the dashboard on the driver's side.
4. Connect your scan tool to the OBD-II port.
5. Follow the instructions on the scan tool to perform a full diagnostic scan of the vehicle. This will help to identify any remaining fault codes that need to be addressed.
6. Once the scan is complete, navigate through the scan tool's menu options to find the feature to clear or reset trouble codes.
7. Select the "Clear Codes" or "Erase DTCs" option, and confirm that you want to delete all fault codes.
8. Disconnect the scan tool from the OBD-II port.
9. Start your 1999 Mercedes-Benz 500 SL and observe whether the check engine light has been reset and turned off.
Note: If the check engine light illuminates again after you have reset it, this indicates that there may still be an unresolved underlying issue with your vehicle's emission system or engine. It is recommended to have the issue diagnosed by a qualified Mercedes-Benz mechanic or technician.
