All the components on the steering wheel are controlled by the steering column switch center unit (SZL). The SZL is divided into two electronic modules. One is located in the steering wheel and the other is attached to the steering column. Both units are connected by means of spiral spring.

The SZL contains no ISIS sensors and is responsible for deploying the drivers airbag.

Fig 1: Identifying Steering Column Switch Center (SZL)

Courtesy of BMW OF NORTH AMERICA, INC.

The SZL is integrated in the steering column electronics and linked to the SIM via the bytelight. The power supply of the SZL is also from the SIM and it is buffered by the memory backup capacitor.

In addition, there is a KL 30 for the supply of circuit elements not relevant to safety (e.g. steering wheel heating) and a KL 15 "ON" from the CAS for redundancy.

In sleep mode of the byteflight , the power supply of the SZL is deactivated by the SIM. The watchdog function is run by the SIM.

Fig 2: Steering Column Switch Center (SZL) Circuit Diagram

Courtesy of BMW OF NORTH AMERICA, INC.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Steering Column Switch Center (SZL)

Use the Manual With the Right Hardware

When to See a Mechanic

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