How to Troubleshoot the Check Engine Light of a BMW 540i


1. Open the driver's side door and place the BMW's keys into the ignition. Don't turn the key or start the car. Just leave the keys there for later use.
2. Connect the BMW's diagnostic outlet with a diagnostic scanner. You will find this outlet beneath the BMW's dashboard.
3. Turn the key in the ignition. Try turning on the electrical system only, and wait to see if a code pops up on the scanner. If it doesn't, start the BMW's engine.
4. Read the codes that appear on the scanner, and write them down.
5. Turn the BMW off, and disconnect the diagnostic scanner. Exit the vehicle.
6. Go to the OBD-Codes.com BMW website, and look up the code on its list of codes (see Resource). If it is not listed there, you can call a local auto parts store. Most will look up codes for customers as a free service.