Lambda Control, Basic Function - GF07.10-P-1054A

Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 
  • Lambda control 
  • Closed-loop control circuit 
  • Two-sensor control 

General 

The lambda control monitors exhaust gas conversion in the catalytic converters. As a result, the maximum volume of exhaust gases is converted into carbon dioxide (CO₂ ), water (H₂ O) and nitrogen (N₂ ).

Function requirements 

• Engine management ON (circuit 87M)
• Engine in operation
• Coolant temperature (depending on operating status)
• Operating temperatures of oxygen sensors are reached
• Overrun mode fuel shutoff deactivated

Function 

Lambda control 

For optimum exhaust gas conversion, the fuel/air ratio must be made to approximate an air index of lambda (λ) = 1. The oxygen sensors upstream and downstream of the catalytic converter detect the oxygen and nitrogen oxide content in the exhaust gas. In the process, they compare the oxygen concentration in the exhaust gas with the oxygen concentration in the ambient air.

In exhaust gas technology, the variable lambda (λ) stands for the mass ratio of air to fuel in the combustion process. A differentiation is made here between the following conditions:

• Low oxygen content (rich mixture): λ ≤1
• Stoichiometric ratio (ideal mixture): λ = 1
• High oxygen content (lean mixture): λ ≥1

Closed-loop control circuit 

Courtesy of MERCEDES-BENZ USA

Closed-loop control circuit 

The oxygen sensor element upstream of the catalytic converter responds to the oxygen content in the exhaust gas and sends a linear voltage signal to the combustion engine control unit that corresponds to the lambda value.

If the oxygen content is too high (lean mixture), the combustion engine control unit initiates an increase in the injection quantity to the cylinders through the fuel injectors. As a result, the oxygen content in the exhaust gas decreases and the fuel/air ratio alters in the direction λ = 1.

If the oxygen content is too low (rich mixture), the combustion engine control unit initiates a reduction in the injection quantity to the cylinders through the fuel injectors. As a result, the oxygen content in the exhaust gas increases and the fuel/air ratio alters in the direction λ = 1.

Due to the permanent adjustment of the oxygen content in the fuel/air mixture, a closed-loop control circuit is created. In order to avoid noticeable problems in the handling characteristics, the combustion engine control unit carries out the adjustments slowly. If the mixture is leaned out, the lambda control factor alters in a positive direction. If the mixture is enriched, the lambda control factor alters in a negative direction.

Two-sensor control 

The two-sensor control also has the following function requirements:

• Two-sensor control for the operating temperature of the catalytic converter achieved
• Lambda control active
• Oxygen sensor downstream of catalytic converter fault-free The two-sensor control monitors the function of the oxygen sensor upstream of the catalytic converter as well as the effect of the catalytic converter, with an additional oxygen sensor downstream of the catalytic converter (guide and diagnostic sensor). The combustion engine control unit determines the mean lambda value from the signals of the oxygen sensor element downstream of the catalytic converter (guide and diagnostic sensor). The mean lambda value is compared with the signals of the oxygen sensor upstream of the catalytic converter and a stored specified value. If the variance is too large in several measurements, this leads to a self-adjustment of the mixture formation with the aid of a correction value. If the correction value exceeds the prescribed limit value and if the following sources of error are excluded for the mixture formation then the oxygen sensor upstream of the catalytic converter must be replaced.

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

• Unmetered air due to leaks in the exhaust system upstream of the oxygen sensor
• Wear or carbon deposits on the fuel injectors,
• Defective sensors or actuators
• Engine wear (e. g. leaky valves)

If the prescribed limit value is exceeded, the instrument cluster displays a fault message. Exceeding of the limit value is stored in the fault memory by the combustion engine control unit.

In engines with a 3rd lambda sensor, it is needed to monitor the regeneration of the gasoline particulate filter. The 3rd lambda sensor is located downstream of the gasoline particulate filter and the second three-way catalytic converter. If excessive soot content is detected in the gasoline particulate filter, active regeneration is performed depending on the operation.

	Function schematics
	Function schematic for lambda control	Engine 260, 282 in model 118, 177, 247 Engine 264 in model 167	PE07.10-P-2511-97A
		Engine 176, 177 in model 167 Engine 177 in model 290 as of model year 2021	PE07.10-P-2511-97B
		Engine 256 in model 167 Engine 264 in model 213, 238, 257 as of model year 2021	PE07.10-P-2511-97C
		Engine 139 in model 118, 177, 247	PE07.10-P-2511-97D
		Engine 254 in model 206, 214, 254	PE07.10-P-2511-97E
		Engine 176 in model 223	PE07.10-P-2511-97F
		Engine 256 in model 223	PE07.10-P-2511-97G
		Engine 279 in model 223	PE07.10-P-2511-97H
		Engine 139 in model 192, 206, 232	PE07.10-P-2511-97I
		Engine 177 in model 192, 223, 232	PE07.10-P-2511-97J
		Engine 274 in model 213 as of model year 2021	PE07.10-P-2511-97K
	Additional basic functions
	Self-adjustment of mixture formation, basic function	Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282	GF07.10-P-1055A
	Lambda sensor, basic function	Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282	GF07.04-P-2000A