ME-SFI TWC heating-up, function - GF07.61-P-3032V

ENGINE 273.961 in MODEL 216, 221 up to Model Year 8 

Model 171 shown with engine 272.963 

Fig 1: ME-SFI TWC Heating-Up Function Diagram

Courtesy of MERCEDES-BENZ USA

The TWC heating-up function heats up the catalytic converters more rapidly to their operating temperature (300 to 450°C) and thus considerably reduces the exhaust emissions in the cold start and heating-up phase.

The ME control unit is able to detect that the operating temperature has been reached and that the catalytic converters are operating at normal efficiency from the signals supplied by the O₂ sensors.

The following conditions determine whether TWC heating is enabled:

• Engine starting temperature
• Altitude level
• Residual heat in the catalytic convertor (from theoretical calculation)
• Difference between intake air and engine starting temperatures
• Air mass

The following systems are involved in the TWC heating-up:

• Ignition system

  At idle speed and coolant temperature dependent, the ignition angle is retarded for e.g. 20 seconds and thus the exhaust temperature is increased.

• Idle speed control

  Dependent on coolant temperature, the idle speed is increased to approx. 1100 to 1300 RPM for a maximum of 20 seconds.

• Camshaft adjustment

  For TWC heating, special positions are specified separately for the intake and exhaust camshafts

• Coolant-temperature dependent transmission shift delay is retarded for automatic transmissions.
• Secondary air injection

After starting and during warm-up, the enriched mixture results in more unburned hydrocarbons in the exhaust. The injected air (high oxygen concentration) causes post-oxidation in the catalytic converters. Heat is released as a result, which more rapidly warms up the catalytic converters to operating temperature.