BMW Tech Tip: Ignition Lock Spins Freely – UnderhoodService

BMW Tech Tip: Ignition Lock Spins Freely

The ignition lock cylinder on E31, E36, E38 and E39 models built prior to January 1999 was designed with an actuating tab that breaks off if forcing of the lock is attempted with the wrong key, or with some form of tool as part of a vehicle theft effort.

The ignition lock cylinder on E31, E36, E38 and E39 models built prior to January 1999 was designed with an actuating tab that breaks off if forcing of the lock is attempted with the wrong key, or with some form of tool as part of a vehicle theft effort.

The purpose of the breakaway tab is to prevent the lock assembly from being forced to the point where the cylinder breaks out of the housing, allowing the steering lock to release and the ignition switch to be turned with a screwdriver. Since the cylinder will spin freely, the required force cannot be applied to the assembly.

It’s possible to break off the tab if enough force is applied to the proper key, and the key has not been inserted completely into the cylinder. Even if the tab has been broken off, the lock will still operate, as long as the correct key is completely inserted into the lock.

Service Procedure:
If the tab has been broken off, the lock cylinder can be replaced, following repair manual instructions, Section 32 32 050. When the cylinder is removed, carefully inspect the inside of the housing to locate the tab and remove all broken-off pieces. It’s normally not necessary to replace the housing unless damage to the inside of the housing is evident.

Courtesy of ALLDATA.

For additional information, visit www.alldata.com.

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Ignition Coil Output

To see inductance inside the primary windings, use an amp probe placed around the positive wire for the ignition coil.

Kilovolts or kV is the unit used to measure the output of an ignition coil. Some coils can output 20kV to 40 kV. So, how does an ignition coil turn system or battery voltage into these huge voltages? The answer is inductance. 

The ECM provides the voltage to the primary coil winding. The primary winding might have 100 turns around the coil’s core or plates. When the voltage to the coil is turned off, a magnetic field collapses. The collapsing field will generate more than 100 volts thanks to inductance. The energy is transformed by the windings in the secondary with inductance again, but thanks to the 10,000 windings, the voltage is boosted to 40kV at the spark plug’s electrodes. The best way to see inductance inside the primary windings is to use an amp probe placed around the positive wire for the ignition coil. With this setup, you can see the current ramping in the coil and the collapse of the magnetic field. 

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