SAAB WIS ONLINE

Engine torque limitation

Engine 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 85 (4.1) or 21 (5.2), or to Saab Trionic engine control module pin 13. 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.

The signal between the control modules is different for 4-cyl. and 6-cyl. engines.

4-cyl engines

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 V (ground) for a period of time which is proportional to the requested torque reduction. The maximum length of time for this is 250 ms.

6-cyl. engines

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 V (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 give rise to ignition timing angles between -5° and +30°. The pulse duration of the above corresponds to between 0.9 ms and 9.2 ms.