SID feeds the steering wheel controls with +5V via pin 22 and grounds though pin 9. The 9 steering wheel control switches comprise 9 resistors connected in series. Pressing the button will ground the associated contact. See table under "SID". Depending on which switch is pressed the aggregate resistance in the circuit is changed and thereby the voltage which SID senses. SID receives information from SWC on the gear selected by the driver in position M. This information is forwarded from SID pin 10 to TCM pin 8 (A) by means of SID sending out specific voltage values as per below:

Hold Gear, Voltage between 0.5V-1.4V
Shift Gear -UP, (+) Voltage between 1.4V-1.79V
Shift Gear -Down, (-) Voltage between 2.7V-3.5V

When the ignition is on SID continuously sends a voltage between 0.5-1.4V corresponding to Hold Gear. If the driver presses Shift Gear -Up (+) or Shift Gear -Down (-) the voltage is raised to between 1.4V-1.79V (+) or 2.7V-3.5V (-) during the time the button is pressed down. When the driver releases the button SID returns to sending out between 0.5V.1.4V i.e. the Hold Gear function. The driver must press the + or - buttons for more than 20 msec before shifting can take place. TCM ignores the signals if position M is not selected with the selector lever.

Fig 1: Wiring Diagram - Sentronic

Courtesy of SAAB-SCANIA OF 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.

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