(Lambda Control, Function - GF07.10-P-1010MMG)

ENGINE 276.8/9 in MODEL 166 

up to model year 2016 

Function requirements for lambda control, general points 

• Circuit 87M (engine management ON)
• Engine runs
• Coolant temperature > -10°C
• Operating temperature reached in left and right oxygen sensors upstream of catalytic converter (G3/3, G3/4)
• Deceleration fuel shutoff not active

Lambda control, general points 

The mixture composition in homogeneous mode is controlled within the narrow limits around λ = 1 in order to achieve a high conversion of the exhaust gases (exhaust gas conversion) in the catalytic converters. For engine 276.9 with stratified operation (with code 920 (Gasoline direct injection with stratified charge)) the ME-SFI [ME] control unit (N3/10) regulates to a lean mixture λ > 1 based on a characteristics map, to lower the fuel consumption.

To do this the CDI control unit (N3/10) reads in signals from the following components:

• Coolant temperature sensor (B11/4), coolant temperature
• Pressure sensor downstream of throttle valve (B28/7), engine load
• LH and RH oxygen sensors upstream of catalytic converter
• Hot film MAF sensor (B2/5), (for code 920 (Gasoline direct injection with stratified charge)), exhaust gas recirculation rate

Exhaust gas conversion in three-way catalytic converter 

Courtesy of MERCEDES-BENZ USA

Function sequence for lambda control 

Lambda control is described in the following points:

• Function sequence for closed-loop control circuit 
• Function sequence for two-sensor control 
• Function sequence for oxygen sensor heater 
• Function sequence for self-adjustment of the mixture formation 
• Function sequence for catalytic converter monitoring 

Function sequence for closed-loop control circuit 

The oxygen sensors upstream of the catalytic converter respond to the oxygen content in the exhaust and send corresponding signals to the ME-SFI [ME] control unit.

For a low oxygen content in the exhaust (λ < 1), the oxygen sensor transmits the signal "rich mixture" to the ME-SFI [ME] control unit. This then reduces the injection quantity through regulation of the fuel injectors (Y76) and alters the mixture composition in the direction "lean". The oxygen content in the exhaust increases and the value alters in the direction λ=1.

When the oxygen content in the exhaust is high (λ > 1), the oxygen sensor sends the "lean mixture" signal to the ME-SFI [ME] control unit. This then increases the injection quantity through regulation of the fuel injectors and alters the mixture composition in the direction "rich". The oxygen content in the exhaust decreases and the value alters in the direction λ=1.

This process is repeated (control loop). The ME-SFI [ME] control unit alters the mixture composition with a time delay in order to prevent any risk of jerking.

For engine 276.9 with stratified operation (for code 920 (Gasoline direct injection with stratified charge)), a lean mixture is regulated with λ > 1 according to a stored characteristics map.

The regulation status is displayed in Xentry Diagnostics based on a lambda control factor which changes in a positive direction for leaning of the mixture and in a negative direction for enriching of the mixture.

Additional function requirements for two-sensor control 

• Operating temperature of catalytic converters reached
• Lambda control active
• Left and right oxygen sensors downstream of catalytic converter (G3/5, G3/6) are error-free

Function sequence for two-sensor control 

The two-sensor control monitors the function of the left and right oxygen sensors upstream of the catalytic converter and the effectiveness of the catalytic converters.

To do this the ME-SFI [ME] control unit reads in signals from the following components:

• LH and RH oxygen sensors upstream of catalytic converter, oxygen sensor signals
• LH and RH oxygen sensors downstream of catalytic converter, oxygen sensor signals

The ME-SFI [ME] control unit determines the lambda mean value using the oxygen sensor signals downstream of the catalytic converter. This value is compared with a stored value for optimum exhaust emissions.

If the deviation is too large after a number of measurements, a correction value is determined for the lambda control.

Using the correction value (value for new left and right oxygen sensors upstream of catalytic converter is about 0), aging of the oxygen sensors upstream of the catalytic converter is adjusted for within certain limits.

The correction value depends on the performance map and the ME-SFI [ME] control unit applies it by adaptation of the injection period of the fuel injectors. If the correction value exceeds the prescribed limit value and if the following error causes are excluded for the mixture formation then the oxygen sensors upstream of CAT must be replaced.

The following errors can, for example, occur during mixture formation:

• Unmetered air due to leaks in the exhaust system upstream of the oxygen sensors
• Wear or carbon deposits on the fuel injectors,
• Damaged hot film mass air flow sensor (with code 920 (Gasoline direct injection with stratified charge))
• Damaged pressure sensor downstream of the throttle valve
• Damaged fuel pressure and temperature sensor (B4/25)
• Damaged oxygen sensors
• Damaged purging switchover valve (Y58/1)
• Wear on the engine (e.g. valve leaky)

If the specified limit value is exceeded or if the plausibility check of the sensor signals (upstream or downstream of CAT) is negative, the ME-SFI [ME] control unit actuates the engine diagnosis indicator lamp (A1e58) in the IC (A1) via the chassis CAN 1 (CAN E1) and chassis CAN 2 (CAN E2). Exceeding of the limit value is stored in the fault memory by the ME-SFI [ME] control unit and can be read out and deleted using the Xentry Diagnostics.

Function sequence for oxygen sensor heater 

The oxygen sensor heaters bring the oxygen sensors up to operating temperature more quickly. With controlled heating, they also prevent damage to the oxygen sensor ceramics.

The oxygen sensor heaters differ according to lambda sensor type:

• Wideband oxygen sensor
• Narrow band oxygen sensor

Wideband oxygen sensor

The left and right oxygen sensors upstream of the catalytic converter are heated continuously when the engine is running, in order to keep them functioning.

Temperature control and temperature measurement (by measuring the internal resistance) is performed by special control electronics in the ME-SFI [ME] control unit.

Narrow band oxygen sensor

Using a ground signal, the ME-SFI [ME] control unit actuates and synchronizes the oxygen sensor heaters for the left and right oxygen sensors downstream of the catalytic converter.

For this purpose the ME-SFI [ME] control unit reads in the signal from the coolant temperature sensor.

When the exhaust system is very cold (while condensation is present), the oxygen sensor heaters are switched off to prevent damage (due to thermal shock).

Additional function requirements self-adjustment of the mixture formation 

• Lambda control active
• Engine at idle or in partial load
• Engine in homogeneous mode

Function sequence for self-adjustment of the mixture formation 

For regulated catalytic converters, the lambda control determines the injection period so exactly that a specified air/fuel ratio (λ) is maintained under all operating conditions.

Self-adjustment ensures that the mixture composition in the open-loop operation (e.g. warm-up phase) is neither too rich nor too lean. It also prevents the lambda control from coming to the end stop at high altitudes.

If a fault occurs, the ME-SFI [ME] control unit automatically makes a correction of the mixture formation. In this case, the lambda characteristics map is shifted within the specified control limits so that the lambda control is not at the upper or lower end stop.

If the mixture composition is constantly drifting out of the central controlled range, the ME-SFI [ME] control unit shifts the lambda characteristics map under certain operating conditions until the lambda control factor is about 0.

Shifting of the lambda characteristics map 

Courtesy of MERCEDES-BENZ USA

Shown with self-adjustment value with Xentry diagnostics 

The following can be read out with Xentry diagnostics:

• Shifting of the lambda characteristics map
• Direction of shift (rich or lean)
• Size of the shift

Presentation takes place in the form of a factor and means that the measured air mass value is multiplied by the factor.

Example:

Measured air mass: 150.0 kg/h

Displayed factor in Xentry diagnostics: 1.1

The ME-SFI [ME] control unit uses a mathematical air mass value of 165 kg/h (150 kg/h x 1.1) to determine the injection period (fuel injection quantity).

The maximum correction values are -0.68 to +1.32.

Additional function requirements for catalytic converter monitoring function sequence 

• Operating temperature of catalytic converters reached
• Lambda control active

Function sequence for catalytic converter monitoring in general 

The law maker requires that the hydrocarbon (HC) emissions do not exceed a certain value. It is therefore necessary to constantly check the catalytic converters for aging.

Aging of a catalytic converter arises from the oxygen storage capacity reducing over time and the subsequent resultant reduced HC conversion.

The catalytic converter stores oxygen during the leaning of the mixture (control loop) and releases it again during enrichment of the mixture for HC conversion.

Function sequence for catalytic converter monitoring 

To check the oxygen storage capacity, a rich mixture (λ < 1) is issued until the left and right oxygen sensors downstream of the catalytic converter have reached a specific maximum value and the greatest portion of the oxygen is removed.

A lean mixture (λ > 1) is then issued and the time is measured to see how long it takes until the left and right oxygen sensors downstream of the catalytic converter have reached a specific minimum value and the catalytic converter has filled up its oxygen storage capacity.

If the time measured lies below a stored characteristic then the oxygen storage capacity is inadequate and an error is stored in the ME-SFI [ME] control unit.

	Electrical function schematic for lambda control		PE07.10-P-2710-97NAE
	Overview of system components for gasoline injection and ignition system with direct injection	ENGINE 276.9 in MODEL 166 up to model year 2016	GF07.70-P-9998MMG
		ENGINE 276.8 in MODEL 166 up to model year 2016	GF07.70-P-9998MMU