In case plug lead 6 or 12 (the ones with the inductive pickup donuts on them) are disconnected or short, a protection circuit embedded within the Motronic will severely clip the duty cycle of the injectors for that side to protect the catalysts from being drenched in raw, unburned fuel.


Catalytic converter protection function
Ignition circuit monitoring

The ignition circuit is monitored by the cylinder detection sender (pin 16) on ignition line 6 (or 12). If it detects no ignition signal on ignition line 6 (or 12) , the fuel supply to to the relevant cylinder bank is cut out by shortening the injection signal. The sender monitors the entire primary side of ignition, and cylinder 6 or 12 on the secondary side.
The inductive sensor is outlined in red above.

http://www.fibersonde.com/e31/images...catprotect.jpg