Emission Control Systems — General Information (Opel Astra H)

In order to reduce the level of emissions into the atmosphere of toxic components that enter the engine exhaust gases as a result of evaporation and incomplete combustion of fuel, and to comply with environmental standards, the models considered in this Manual are equipped with a number of special systems that could be combined under the general name of engine management and exhaust gas toxicity reduction systems.

Systems related to engine management and exhaust gas toxicity control include the following:

• a) On-Board Diagnostics (OBD) system - see Chapter 5;
• b) Electronic Engine Management System (ECM) - see Chapter 5;
• c) Positive Crankcase Ventilation (PCV) system;
• d) Exhaust gas recirculation (EGR) system;
• e) Evaporative emission control system (EVAP);
• f) Catalytic converter and lambda probe (exhaust gas composition control).

The sections below provide general descriptions of how each system operates.

Diagnostics of emission control system components controlled by electronic devices requires the use of special, complex-to-use equipment and a certain qualification of the performer, and therefore, it would be reasonable to entrust its implementation to professional mechanics of a specialized service station. The above does not mean that maintenance and repair of emission control system components in practice seem difficult to perform. Do not forget that one of the most common causes of failures is an elementary violation of the quality of vacuum or electrical connections, and therefore, first of all, you should always check the condition of the nipples and electrical connectors. The car owner can independently and quite easily perform a number of checks, as well as perform many routine maintenance procedures for most system components at home, using a standard set of adjustment and plumbing tools.

Crankcase ventilation system (PCV)

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The PCV system serves to reduce the emission of hydrocarbon compounds into the atmosphere by removing crankcase gases from the engine. The block is purged by running fresh air from the air cleaner through the crankcase, where it mixes with accumulated vapors and gases that have broken through the combustion chambers and is removed through the PCV valve into the intake manifold.

The main components of the system include the PCV valve, purge filter, and a set of vacuum hoses that connect these devices to the engine.

In order to maintain stable idle speed, the PCV valve closes the purge flow when there is a deep vacuum in the intake manifold. In the event of a malfunction of the engine (such as when piston rings wear out) the system removes excess crankcase gases through the ventilation tube back to the air cleaner.

Exhaust gas composition control

See also Chapter "Controls and operating techniques", Section 28.

In order to minimize the emission of toxic components into the atmosphere, a catalytic converter is included in the exhaust system. Control is carried out by a closed-type control system. Feedback with the engine control system is organized by means of a lambda probe mounted in the exhaust system's intake pipe.

A catalytic converter is a component of exhaust gas toxicity reduction systems, is included in the exhaust system and serves to reduce the emission of toxic components into the atmosphere. The vehicles discussed in this Manual use two types of catalytic converters. A conventional oxidation converter reduces the content of hydrocarbons and carbon monoxide in the exhaust gases. A three-function catalytic converter additionally reduces the emission of nitrogen oxides (NO_x).



Lambda probe (oxygen sensor) monitors the oxygen content in the exhaust gas flow. When O ₂ molecules come into contact with the sensitive element of the probe, the sensor generates an amplitude signal depending on the oxygen concentration. The electronic module of the engine management system continuously monitors the signals coming from the lambda probe, if necessary issuing commands to adjust the composition of the air-fuel mixture by changing the duration of the opening of the injection injectors. Two lambda probes are used on the models of cars under consideration; the primary is located in the engine exhaust manifold, and the secondary is below the catalytic converter. By comparing the oxygen levels in the exhaust tract above and below the catalytic converter, the engine management system also determines the efficiency of the latter.

Evaporative Emissions (EVAP) System

The system accumulates evaporation in the fuel tank and ensures its output into the intake manifold for combustion during normal engine operation. The general principle of operation of the EVAP system is described below. The described design does not necessarily have to fully correspond to the design of the system installed on a specific car, but the principle of operation is common to all models.

Any EVAP system necessarily includes a special adsorber filled with activated carbon, which actually collects fuel vapors. The method of removing vapors from the adsorber may vary depending on the design of a specific system.



The fuel filler cap is equipped with a two-way safety valve. In the event of a system failure, the valve ensures that fuel vapors are released into the atmosphere. Another shut-off valve (oRVR valve) is installed near the fuel tank and provides regulation of the removal of fuel vapors into the carbon adsorber depending on the pressure/vacuum drops associated with temperature changes.

On the way to the carbon adsorber, fuel vapors pass through a two-way valve and through ventilation hoses enter the carbon adsorber installed in the engine compartment, where they accumulate while the car engine is turned off.

When the engine is started, the purge solenoid valve of the adsorber remains closed until it warms up to a certain temperature. From the adsorber, fuel vapors are blown out through the diaphragm valve into the intake manifold, from where they enter the combustion chambers, where they are burned out during normal engine operation. The fuel tank is also usually equipped with a sensor that monitors changes in pressure in the tank both when the car is parked and when the car is moving.

Exhaust gas recirculation system

In order to reduce emissions of nitrogen oxides into the atmosphere (NO_x) the engine design provides for the removal of part of the exhaust gases into the intake manifold through the EGR valve. Such mixing of exhaust gases into the air-fuel mixture leads to a decrease in its combustion temperature.

The system consists of an EGR valve, an EGR valve opening degree sensor and a set of auxiliary information sensors. The system is controlled by an electronic module of the engine management system. The module controls the optimal opening degree of the EGR valve for any engine operating conditions. A special information sensor constantly monitors the opening degree of the EGR valve, sending corresponding signals to the control module. The electronic device compares the incoming information from the sensor with the optimal calculated value determined by the data received from other information sensors and, if necessary, makes the required adjustment of the volume of exhaust gases entering the engine.