What it does
The SZL is the switch assembly behind the steering wheel: the turn-signal, high-beam and wiper stalks, the clock spring that carries the wheel buttons and the driver airbag across the rotating joint, and the steering angle sensor. On the E90 it evaluates the turn-signal and high-beam stalk itself and passes the result to the footwell module, which switches the lights.
How it fails, and what gets replaced first by mistake
The clock spring ribbon wears with use. Symptoms arrive together or one at a time: airbag warning, dead steering-wheel buttons, implausible steering-angle readings. The trap is replacing the airbag unit for a warning the clock spring is causing.
Generations this applies to
From a documented source: BMW training ST502, E90 General Vehicle Electrical; bimmerscan.com (FRM); Pelican Parts and YOUCANIC (E90 SZL).
Is this module acting up on your car?
I come to the car, read the modules and trace the fault to the actual wire, connector or module.
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