On the BMW E46 3 series and the BMW E39 5 series, it regularly happens that the airbag light comes on. The cause is a defective sensor mat in the passenger seat. This malfunction is not only very annoying, but also dangerous. Because you not only see a red airbag light all the time, but the passenger’s head airbag doesn’t work.
A solution is to place a new sensor mat in the chair, but this repair is relatively expensive. A cheap – but just as safe – option is to bypass the entire sensor mat with a by-pass unit. This bypasses the sensor mat and the car thinks that there is always someone in the seat. The only difference with replacing the entire sensor mat is that, in the event of an accident, the airbag will also go off if there is nobody in the seat.
After installing the by-pass unit, the error message will be removed from the car using original BMW software, after which the airbag will function again. That annoying light in the instrument cluster is then also off.
With newer BMWs, models such as the E60 / 61 5 series, the E87 1 series and the E90 3 series, the fault can even be resolved without placing a resistor. The airbag malfunction can be solved by coding. The side effect, just like when placing a resistor, is that the airbag will always pop in the event of an accident.
In some cases (5% -10%), the airbag malfunction cannot be eliminated by coding. In that case you obviously do not pay for the procedure. However, the readout rate then applies, you will receive a printout on which exactly is indicated what is defective, so that you can have this part replaced. This happens, for example, when the airbag light is not on because of a defective seat mat, but because of a defective airbag somewhere in the car.