The 540i is a luxury sports sedan that was produced as part of the BMW 5-Series. If you find that the check engine light has come on, that means that the 540i's computer has detected a problem that needs to be corrected. Once you've made the repair, in order to get the check engine light to go off, you'll need to reset the engine codes on your 540i. Removing all the power to the computer will clear the codes, and you can do this easily by momentarily disconnecting the battery.
Turn your 540i off and remove the key from the ignition.
Lift the trunk on your 540i. Open the battery and fuse compartment located on the passenger side of the trunk.
Loosen the negative battery clamp from the battery, using the 10mm socket wrench. The negative clamp is marked with a minus sign. Remove the clamp and wait for one minute.
Reattach the clamp to the battery and tighten it with the 10-mm socket wrench.
Start your 540i and wait for all of the startup warning lights to go off. Confirm that the check engine light goes off too.
Place the cover back on the battery and fuse compartment. Close the trunk.
