LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Mercedes Benz >> 2021 >> G63 AMG >> Repair and Diagnosis >> Engine Performance >> Tune-Up >> Mixture Formation - 463 Chassis (2 Of 4) >> Basic Knowledge >> Lambda Control, Function >> Lambda Control, Function - GF07.10-P-1010MNH
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Lambda Control, Function - GF07.10-P-1010MNH

Engine 176.9, 177.9 in model 463 

as of model year 2019 

Function requirements for lambda control, general points 

IMPORTANT The circuit relay87M (K40/8 kN) is switched on for circuit 15 ON.

Lambda control, general points 

The mixture composition is controlled within narrow limits of approximately λ = 1 in order to achieve high conversion of the exhaust gases (exhaust gas conversion) in the catalytic converters (three-way catalytic converters).

To do this the ME-SFI control unit (N3/10) reads in signals from the following sensors:

Exhaust gas conversion in three-way catalytic converter 

G13655850Courtesy of MERCEDES-BENZ USA

Function sequence for lambda control 

The lambda control function includes the following subfunctions:

Function sequence for closed-loop control circuit 

The left lambda sensors sensor elements and right lambda sensors sensor elements upstream of catalytic converter react to the oxygen portion in the exhaust. The ME-SFI control unit directly reads in the left lambda sensors sensor elements and right lambda sensors sensor elements.

When the oxygen content in the exhaust (λ < 1) is low the sensor elements send the signal "rich mixture" to the ME-SFI control unit. This then reduces the injection quantity through regulation of the fuel injectors for cylinders 1 to 8 (Y76/1 to Y76/8) 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 (λ > 1) is high the sensor elements send the signal "lean mixture" to the ME-SFI control unit. This then increases the injection quantity through closed-loop control of the fuel injectors for cylinders 1 to 8 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 control unit alters the mixture composition with a time delay in order to prevent any risk of jerking.

IMPORTANT The regulation status is displayed in the diagnostic device based on a lambda closed-loop control factor that alters in a positive direction for leaning the mixture and in a negative direction for enriching the mixture.

Additional function requirements for two-sensor control 

Function sequence for two-sensor control 

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

To do this the ME-SFI control unit reads in signals from the following sensors:

The ME-SFI control unit determines the Lambda mean value from signals left and right lambda sensors sensor elements downstream of 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 lambda sensors upstream of catalytic converter = 0), aging of the lambda sensors upstream of the catalytic converter is adjusted for within certain limits. The correction value depends on the performance map and the ME-SFI 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 lambda sensors upstream of CAT must be replaced.

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

If the specified limit value is exceeded or if the plausibility check for the lambda sensor signals (upstream or downstream of catalytic converter) is negative, the instrument cluster (A1) issues a fault message.

Exceeding the limit value is stored in the fault memory by the ME-SFI control unit and can be read out and deleted using a diagnostic device.

Function sequence for lambda sensor heater 

The left lambda sensor heater upstream of the catalytic converter (G3/3r1), the right lambda sensor heater upstream of the catalytic converter (G3/4r1), the left lambda sensor heater downstream of the catalytic converter (G3/5r1) and the right lambda sensor heater downstream of the catalytic converter (G3/6r1) bring the lambda sensors up to operating temperature more quickly. Controlled heating also prevents damage to the lambda sensor ceramics.

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

Function sequence for self-adjustment of the mixture formation 

In regulated catalytic converters, the injection period is calculated so accurately by lambda control 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) 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 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 middle controlled range, the ME-SFI 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 

G13655851Courtesy of MERCEDES-BENZ USA

Shown with self-adjustment value with Xentry diagnostics 

The following can be read out with Xentry diagnostics:

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 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 

Catalytic converter monitoring, general points 

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 is caused by the oxygen storage capacity reducing over time and the reduced HC conversion resulting from this. 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 is output (λ< 1), until the sensor elements of the left and right lambda sensor downstream of the catalytic converter have reached a certain maximum value and the largest part of the oxygen has dissipated. A lean mixture (λ>1) is then output and the time is measured to see how it takes until the sensor elements of the left and right lambda sensors downstream of catalytic converter have reached a certain 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 control unit.

  Electrical function schematic for lambda control   PE07.10-P-2710-97ZGF
  Overview of system components for gasoline injection and ignition system with direct injection   GF07.70-P-9998MNH 
scientia non olet · About LEMON Manuals