GENERAL INFORMATION
The emission control system consists of the following subsystems
- Positive crankcase ventilation (PCV) system
- Evaporative emission system
- Exhaust emission control system
GENERAL INFORMATION (POSITIVE CRANKCASE VENTILATION SYSTEM)
The positive crankcase ventilation (PCV) system prevents the escape of blow-by gases from inside the crankcase into the atmosphere.
Fresh air is sent from the air cleaner into the crankcase through the breather hose to be mixed with the blow-by gas inside the crankcase.
The blow-by gas inside the crankcase is drawn into the intake manifold through the PCV valve.
The PCV valve is designed to lift the plunger according to the intake manifold vacuum so as to regulate the flow of blow-by gas properly.
In other words, the blow-by gas flow is regulated during low load engine operation to maintain engine stability, while the flow is increased during high load operation to improve the ventilation performance.
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GENERAL INFORMATION (EVAPORATIVE EMISSION SYSTEM)
The evaporative emission (EVAP) system prevents fuel vapors generated in the fuel tank from escaping into the atmosphere.
Fuel vapors from the fuel tank flow through the vapor pipe/hose to be stored temporarily in the EVAP canister.
When the vehicle is in operation, fuel vapors stored in the EVAP canister flow through the EVAP purge solenoid, purge port and intake manifold plenum to the combustion chamber.
When the engine coolant temperature is low or when the intake air quantity is small (when the engine is at idle, for example), the engine control module (ECM) brings the EVAP purge solenoid into the OFF state to shut off the fuel vapor flow to the intake manifold plenum. This ensures driveability when the engine is cold or running under low load and also stabilizes the emission level.
An EVAP ventilation solenoid is provided between the EVAP canister and atmosphere to monitor for OBD-II EVAP leaks. This solenoid is normally OFF. However, it turns ON when monitoring for OBD-II EVAP leaks and shuts off the atmosphere flow to the EVAP canister. Then the fuel tank differential pressure sensor monitors the fuel vapor pressure to detect OBD-II EVAP leaks. The fuel overflow limiter valve and the leveling valve prevent fuel from being overfilled. The fuel overflow limiter valve and the leveling valve prevents fuel leaks if the vehicle is rolled over in an accident.
The EVAP ventilation valve releases the air from the fuel tank through the EVAP canister into the atmosphere when the fuel tank pressure increases due to refueling, etc. The EVAP ventilation valve and the air filter supply the atmospheric air to the EVAP canister when the fuel tank pressure decreases.
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Required Special Tool
MB995061: Purge Flow Indicator
- Disconnect the purge hose from the evaporative emission (EVAP) purge solenoid, and connect special tool MB995061 between the EVAP purge solenoid and the purge hose.
- Before inspection, set the vehicle in the following conditions: Engine coolant temperature: 80 - 95°C (176 - 203°F) Lights, electric cooling fan and accessories: OFF Transaxle: Neutral (P range on vehicles with CVT) NOTE: Vehicles for Canada, the headlight, taillight, etc. remain lit even when the lighting switch is in "OFF" position but this is no problem for checks.
- Run the engine at idle for more than four minutes.
- Check the purge flow volume when engine is revved suddenly several times. Standard value: Momentarily 20 cm 3 /s (2.5 SCFH) or more .
- If the purge flow volume is less than the standard value, check it again with the vacuum hose disconnected from the EVAP canister. If the purge flow volume is less than the standard value, check the vacuum port and the vacuum hose for clogging. Also check the EVAP purge solenoid. If the purge flow volume is at the standard value, replace the EVAP canister.
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- Disconnect the inlet manifold from the EVAP purge solenoid valve. NOTE: When disconnecting the vacuum hose, always place an identification mark so that it can be reconnected at its original position.
- Disconnect the harness connector.
- Connect a hand vacuum pump to nipple (A) of the EVAP purge solenoid (refer to the illustration).
- As described in the chart below, check airtightness by applying a vacuum with voltage applied directly from the battery to the EVAP purge solenoid valve and without applying voltage. BATTERY POSITIVE VOLTAGE AND NORMAL CONDITION REFERENCE BATTERY POSITIVE VOLTAGE NORMAL CONDITION Applied Vacuum leaks Not applied Vacuum maintained
- Measure the resistance between the terminals of the EVAP purge solenoid. Standard value: 22 - 26 ohms [at 20°C (68°F)]
- Replace the solenoid if airtightness or resistance is out of specification.
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GENERAL INFORMATION (EXHAUST GAS RECIRCULATION SYSTEM)
The exhaust gas recirculation system (EGR) lowers the nitrogen oxides (NOx) emission level. When the air/fuel mixture combustion temperature is high, a large quantity of NOx is generated in the combustion chamber. Therefore, this system recirculates part of exhaust gas from the exhaust port of the cylinder head to the combustion chamber through the intake manifold to decrease the air/fuel mixture combustion temperature, resulting in reduction of NOx. The EGR flow rate is controlled by the EGR valve (Stepper Motor) for driveability quality.
OPERATION
When the engine coolant temperature is low, when the engine is at idle or when a wide open throttle operation is performed, the EGR valve (Stepper Motor) is kept closed, achieving no EGR. After warming up the engine, the EGR valve (Stepper Motor) can be opened by the engine control module (ECM).
The ECM monitors the EGR system and illuminates the Malfunction Indicator Lamp (SERVICE ENGINE SOON or Check Engine Lamp) to indicate that there is a malfunction.
