Emission Control on Models with Catalytic Converter

OPERATION
To maintain the optimum degree of efficiency of the catalytic converter, this system aims at achieving the ideal air-fuel ratio (lambda = 1) for combustion. The heated oxygen sensor is used for this purpose which measures the residual oxygen content in the exhaust gas and sends a corresponding voltage signal to the control unit. Here, the mixture composition is corrected if necessary by changing the injection timing. In the case of failure of the oxygen sensor, the Digital Motor Electronic (DME) control unit controls the system with a substitute value (0.45 V) preprogrammed in the control unit.

Since a temperature of approx. 300° C is necessary for efficient operation of the oxygen sensors, power is supplied via a relay to a heating resistor in the oxygen sensor. The relay is activated by the DME control unit.

On 12-cylinder engines, both heating resistors in the oxygen sensors receive their voltage supply via one relay. The relay is activated by the DME control unit I.

This relay will no longer be fitted in series production. On models without oxygen sensor heating relays, the sensor heating systems will be activated directly by the Fuel Pump Relay (EKP).