Torque Limitation

When shifting between certain gears, engine torque is reduced in order to make shifting smoother and reduce wear on the transmission.

To check this, the transmission control module sends a signal from pin 13 to Motronic engine control module pin 21.

The transmission control module knows when to shift gear and informs the engine control module to this effect. Torque limitation is then performed by the engine control module. It does this by retarding the ignition timing, which has the effect of reducing engine torque.

Normally, the signal lead carries battery positive voltage (B+). When the transmission control module requests torque limitation, it reduces the current on pin 13 to 0 volts (ground) by means of a 100 Hz PWM signal. The pulse ratio is proportional to the requested torque reduction.

The transmission control module can generate 8 predetermined pulse ratios between 9% and 92%, which should result in ignition timing angles between -5° and +30°.

The pulse duration above corresponds to between 0.9 ms and 9.2 ms.