The task of ignition circuit monitoring is to detect misfiring cylinder-selectively (self-diagnosis) and to prevent damage to the catalytic converter. Exhaust gas emissions cannot deteriorate because fuel injection is cut out for the cylinder concerned.
The secondary circuit monitoring feature operates with a "shunt" (resistor in the common secondary ground line of the 8 ignition coils).The voltage progression at the shunt is transferred to the control unit for each cylinder.
If after successful ignition (cylinder-selective primary circuit monitoring OK.) the threshold voltage for misfiring detection (5V) is not reached, the defect code is set, the defect lamp activated (US models only) and the relevant injection output stage is switched off.