Steering wheel controls: Notes

Fig 1: Steering Wheel Controls Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Steering Wheel Controls Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The steering wheel controls consist of 3 units (7 switches) mounted in the steering wheel and airbag module. The steering wheel controls give the SID unit information on which contacts are activated.

The SID unit supplies the steering wheel controls with +5 V via pin 18 and grounds them through pin 3.

The 7 steering wheel switches consist of 7 resistors connected in series. When a button is pressed, the switch concerned is grounded, see table below.

Depending on which button is pressed, the aggregate resistance in the circuit varies and with it the voltage detected by the SID unit.

The horn switch (41) is connected in parallel with the steering wheel switches and when it is pressed, pin 18 is grounded direct to pin 3.

The table shows the correlation between the voltage on pin 18 and the switch that is activated.

The SID unit uses the information to activate the horn and send bus information for the audio functions. On cars without steering wheel controls (cars without audio system), only the steering wheel switch for the horn is used.