ProStreetDriver

Video tutorial on how to test the ignition switch on a BMW E39. A similar switch is also found on the E38 as well, but may apply to other BMW models too. This is a free method to test the switch to determine if it is causing any issues on your vehicle as it can be very costly to replace. A faulty ignition switch can cause computer errors, some option errors throughout the vehicle, battery drain, or no start. Removing the steering column cover is required in order to gain access to the switch. If the switch is faulty, it can be repaired instead of purchasing a new unit. This particular tutorial was done on a 1997 BMW 540i.

Tools/Supplies Needed:
-phillips screwdriver
-multimeter
-jumper wire

Procedure:
-start by removing the top and bottom plastic phillips screws holding in the clips which hold the steering column caps in place
-once removed, slowly work at removing the steering column caps
-tilt steering wheel when necessary
-after the steering column caps have been separated, unclip the leather covers from the rear both on the top and bottom
-tilt steering wheel when necessary
-using a jumper wire, attach it to a good sourced ground and then connect that to the ground test probe
-select the two place voltage setting on your multimeter
-test the battery voltage so we have a benchmark value
-with the switch in the off position, using the positive probe, touch the terminals on the backside of the ignition switch
-the three middle terminals on the plug are constant power and should have 12v present (or close to what was read on your battery voltage)
-test the outer six terminals and there should be no voltage present
-if there is a small amount of voltage present, there is a short on the terminal and this would indicate a battery drain
-next with the ignition switch in the on position, test the outer six terminals, all will be on except the starter terminal which is indicated by a yellow and black wire, but may vary on different models
-five terminals should have 12v present (or close to your battery voltage)
-if there is no voltage present or much less, there is an issue with the contacts inside the switch assembly
-next turn the key in the start position and test the starter terminal
-there should be 12v (or close to your battery voltage), if not then there is an issue with the terminal inside the ignition switch assembly
-with the switch removed, you can also test continuity across the terminals
-each of the three circuits are in line, therefore always keep on test probe on the center, and test the outside of the switch
-you will need to rotate the internal switched component to activate different positions in the ignition switch
-although a continuity test does work, it isn't as effective as a voltage test