Monitoring catalytic converter efficiency, function - GF49.10-P-3033V

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ENGINE 272.967 in MODEL 164, 251

ENGINE 273.923 in MODEL 164

ENGINE 273.943 in MODEL 164

ENGINE 273.963 in MODEL 164, 251

Shows model 171

Fig 1: Monitoring Catalytic Converter Efficiency, Function Diagram - Shows Model 171

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Each catalytic converter is evaluated on the basis of its ability to store oxygen. The oxygen stored during the lean phase is then reduced totally or partially during the rich phases. Aging reduces the ability of catalytic converters to store oxygen. It also reduces the ability to convert HCs.

By law, HC emissions must not go above certain limits. The task of the catalytic converter monitoring is to evaluate aging through the ability to store oxygen and therefore to convert hydrocarbons.

Active diagnosis depends on direct measurement of the oxygen stored during the transition from rich to lean mixture, when the catalytic converter is at operating temperature and the lambda control is enabled. Several measurements are taken in the lower partial load range.

The wide-band-lambda sensor is located upstream of the catalytic converter, and is used to obtain precise measurements of the mixture. Downstream of the catalytic converter is a lambda discrete sensor, which identifies its current condition.

During the first stage, the oxygen stored when the mixture is rich (lambda about 0.95) is reduced until the sensor voltage downstream of the converter is over about 650 mV.

The next stage switches to the lean mixture (lambda about 1.05) and monitors how long it takes until the sensor voltage downstream of the converter is below about 200 mV.

If the length of time measured in this way is below the value set as the borderline characteristic for catalytic converters, then oxygen storage capacity is insufficient and the converter must be replaced.

If a fault is detected, the engine diagnosis indicator lamp or the "CHECK ENGINE" indicator lamp is lit on the instrument cluster.

The stored faults can be read out and erased with the STAR DIAGNOSIS.

Component description for the O₂ sensors	O₂ sensors upstream of TWC	GF07.04-P-6100V
	O₂ sensors upstream of TWC	GF07.04-P-6100VA
Component description for the ME-SFI [ME] control unit		GF07.61-P-6000V
Component description for the three-way catalytic converter		GF49.10-P-2010V
Component description for the "CHECK ENGINE" indicator lamp		GF54.30-P-5011V
Component description for the engine diagnosis indicator lamp	except	GF54.30-P-5010V