General information
The system accumulates fuel vapors accumulating in the power supply system while the vehicle is parked and ensures that they are discharged into the intake pipeline for combustion during the normal operation of the engine.
Any EVAP system necessarily includes a special adsorber filled with activated carbon, which, in fact, collects fuel vapors. The method of removing vapors from the adsorber may vary depending on the design of a particular system. The following description will allow the reader to understand in sufficient detail the principles of operation of any type of EVAP system.
Note. The described design does not necessarily have to fully correspond to the design of the system installed on a particular vehicle, however, the principle of operation is common to all models equipped with a fuel injection system. If any deviations are found, check the information given on the VECI label attached under the hood.
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 vented to the atmosphere.
Other check valve (ORVR valve) installed near the fuel tank and provides adjustment of fuel vapor removal to the carbon adsorber depending on pressure/vacuum drops associated with temperature changes.
On the way to the carbon adsorber, fuel vapors are passed through a two-way valve and through the ventilation hoses they enter the carbon adsorber installed in the engine compartment, where they are accumulated during the entire parking time.
When the engine is started until it warms up to a certain temperature, the canister purge shut-off solenoid valve remains closed, allowing the purge diaphragm valve to open due to an increase in the depth of vacuum in the intake piping. 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 the normal operation of the engine.
The fuel tank is also equipped with a sensor that monitors pressure changes in the tank both during parking and while the car is moving.
Examination
Note. A complete check of the EVAP system is beyond the skill level of the average amateur mechanic. Fortunately, the EVAP system, like other emission control systems, is covered by additional warranties. Most often, failures of the EVAP system are associated with damage to the canister or failure of the vacuum hoses.
1. Always check the condition of the vacuum hoses first, damage or disconnection of which is most often the cause of system failure (refer to the hose routing diagram on your vehicle's VECI label). Replace damaged hoses if necessary.
2. Disconnect the vacuum line from the carbon adsorber and connect a vacuum gauge to the hose. When cold (temperature below 66°C) and the engine idling, there should be no vacuum here, otherwise the condition of the canister purge control solenoid valve should be checked. If there is no vacuum, raise the engine speed to 3000 rpm and warm up the unit to normal operating temperature (cooling fan should run). Now the device should register a vacuum, otherwise, again check the condition of the purge control valve (see paragraph 7).
3. Disconnect the vacuum hose from the two-way EVAP valve (near the carbon adsorber) and connect a hand vacuum pump to it. Make sure the pump is directly connected to the 2-way valve. With the ignition on (do not start the engine), create a vacuum and make sure that the valve holds it securely. The leaky valve must be replaced.
4. With the ignition on (engine not running) disconnect the charcoal canister vent shut-off valve (see accompanying illustration) and make sure the 2-way valve is holding vacuum. If this condition is met, replace the check valve with O-ring. Otherwise, check the wiring in the circuit section between the check valve and the PCM.
5. Disconnect the vacuum hose from the charcoal canister vent shut-off valve, connect a hand vacuum pump and with the ignition on (do not start the engine) make sure the valve does not leak, otherwise replace it.
6. Disconnect the wiring from the charcoal canister vent shut-off valve and with the ignition on (do not start the engine) check for battery voltage between connector terminal #1 and ground. If there is no voltage, check the condition of the wiring between the shut-off valve and the No. 6 15A fuse.
7. Disconnect the 2-pin connector of the canister purge control solenoid valve and with the ignition on (do not start the engine) check for the presence of battery voltage at terminal #1 of the connector. If there is no power, check the wiring in the circuit section between the solenoid valve and the No. 6 15A fuse.
Note. The charcoal canister purge control solenoid valve is located on the left side of the rear bulkhead of the engine compartment (on V6 models), or on the inlet pipeline (on 4-cylinder models).
8. Warm up the engine to normal operating temperature (cooling fan should run). Verify that the vacuum from the purge control solenoid returns to the intake manifold. If there is still no vacuum, disconnect the 2-pin electrical connector and retest the line vacuum. If there is no vacuum this time, check the condition and correctness of the laying of the vacuum hoses. If there is vacuum, check for a short in the wiring between the 2-track connector and the PCM.
9. Disconnect the 2-track connector at the EVAP bypass solenoid valve. With the ignition on (do not start the engine) terminal #1 should have battery voltage. If there is no power, check the wiring in the section of circuit between the valve and the No. 6 fuse at 15 A.
10. Disconnect the 3-pin connector of the electrical wiring of the pressure sensor in the fuel tank and with the ignition on (do not start the engine) measure the voltage between terminals No. 1 and 2 of the connector. Next, measure the voltage between terminals No. 2 and 3. In both cases, the device should register a value of about 5 V. If the test gives a positive result, however, OBD detects a sensor malfunction again, replace the latter.
11. Check the charcoal canister for signs of leakage. Remove the canister assembly and plug all of its vent lines. Connect a hand vacuum pump to the canister vent shutoff valve, apply vacuum and check for leaks. Replace adsorber if necessary.
Replacement
Carbon adsorber
1. Disconnect all ventilation hoses from the adsorber assembly, unscrew the bolts and remove the assembly from under the car. Ensure that all disconnected hoses are properly marked.
2. Installation is carried out in the reverse order.
EVAP 2-way valve, vent shut-off valve, fuel tank pressure sensor, and EVAP bypass solenoid valve
3. To gain access to the listed valves/sensors, remove the carbon canister, then dismantle each of the components individually.
4. Installation is carried out in the reverse order.
Solenoid valve for charcoal adsorber purge control
5. Disconnect the vacuum hoses from the charcoal canister purge control solenoid valve.
6. Turn out a fixing bolt and take the valve from an impellent compartment.
7. Installation is carried out in the reverse order.