Schematic Diagrams And Component Descriptions
Schematic Diagram
Schematic Diagram:
Canister
The Canister is filled with charcoal and absorbs evaporated fuel vapor from the fuel tank. The gathered fuel vapor in canister is drawn into the intake manifold by the ECM/PCM when appropriate conditions are set.
Purge Control Solenoid Valve (PCSV)
The Purge Control Solenoid Valve (PCSV) is installed in the passage connecting the canister to the intake manifold. It is a duty type solenoid valve and is operated by ECM/PCM signal.
To draw the absorbed vapor into the intake manifold, the ECM/PCM will open the PCSV, otherwise the passage remains closed.
Fuel Filler Cap
A ratchet tightening device in the threaded fuel filler cap reduces the chances of incorrect installation, when sealing the fuel filler. After the gasket on the fuel filler cap and the fill neck flange make contact, the ratchet produces a loud clicking noise indicating the seal has been set.
NVLD (Natural Vacuum Leakage Detection)
NVLD (Natural Vacuum Leakage Detection) module is located between the canister and the fuel tank air filter.
The NVLD module is an integral part of the monitoring system. The NVLD module has an internal pressure switch position and a temperature sensor that reports the information to the ECM via on single communication line. The ambient temperature and pressure switch position are checked every 10 minutes during car off for 2 hours.
Evaporative System Monitoring for Smaller Leaks
When the Evaporative System is closed off, any temperature change results in a pressure change. The system monitors the temperature drop as the vehicle is parked and cools off. When the temperature drops and a vacuum builds in the Evaporative System the switch in the NVLD will close. The switch is calibrated to -2.5 +/- 0.3 mbar.
When the switch closes due to a vacuum building in the system, a timer is started in the ECM. Based on the amount of time until the switch opens, the ECM determines a leak.
For Large leak and fuel cap off detection the test is performed during engine running condition.
Evaporative System Monitoring for Large Leak
At first, the OBD-II system checks the vapor generation due to fuel temperature is low enough to start monitoring. Then it pulls a vacuum in the evaporative system by means of PCSV. The PCSV is opened to allow vacuum to close the switch.
The final step is to monitor the switch to see if there is a loss of vacuum to determine is the is a leak in the system.
[Normal Diagnosis]
1. Reading information (READ_INI & INI)
Ready to start diagnosis with initialization. Diagnosis starts with driver's request of vehicle start (key position at start)
When the process starts, ECM reads the NVLD information & failures which are saved during vehicle key OFF period.
The valid air temperature sensing range is -40°C to 120°C. An "out of range" is reported, if the measured temperature is out of this range. After requesting, the memorized values from the NVLD are read. The following information is acquired from the NVLD module; air temperature 6C deviation for at least 2 hour during soaking, checking NVLD switch closed during soaking, air temperature sensor plausibility / electrical failure check, which is detected during soaking, pressure switch electrical failure check during soaking, and reset failures due to power loss
2. Reading information (SW_VERSION)
NVLD sends the 8 bit software version value when the ECM performs a request.
3. Reading Air temperature ( TAM_SWI_DIAG / READ_TAM)
When ECM requests NVLD Air temperature, the measured temperature value is sent to HCU as an 8-bit value.
In case an "out of range" error, maximum or minimum values are received. During the period, whenever ECM requests NVLD pressure switch electrical checking, NVLD returns the current and actual values for the electrical switch error. For the values are red from the NVLD, it is possible to return more than one electrical error at the same time, as all errors could have occurred during engine on phase.
4. Small leakage diagnosis (SMALL_LEAK_DIAG)
To check small leak, ECM requests the saved information from NVLD. During soaking, the resolution of switch closed time is 10min. This means, a maximum time of 2.5h (15 * 10min) can be counted. The switch closed time is reported to the ECM.
5. WAIT
Delay time to wait for the next process
6. Large leakage diagnosis (COMPLETE_DIAG)
At this process, ECM checks large leak with checking switch position. During large leak diagnosis, ECM requests switch position information which includes the current switch position and the switch position transition, which has been monitored since engine run.
7. PCSV plausibility diagnosis (CPS_CHK)
When Large leak error is detected or switch is closed at the beginning of engine start, canister purge valve (PCSV) stuck diagnosis is performed with opening PCSV.
8. STOP
When all of diagnosis are finished, ECM requests STOP mode. During the period, whenever ECM requests NVLD pressure switch electrical checking, NVLD returns the current and actual values for the electrical switch error until end of driving cycle.
9. ERROR
When any error is detected so EVAP monitoring can not be proceeded, ERROR status is performed.
10. OFF
When engine is off with key-off, ECM request STOP status. NVLD is reactivated with a wake-up call at next driving cycle (key position at start). During the period, NVLD checks its timer function and reports error message if any problem is detected.
11. SLEEP
If the key OFF monitoring conditions to detect small leak are not satisfied, ECM requests Sleep status. During the status, no calculations are done in NVLD during the key OFF period.
[EVAP Leak Test Diagnosis]
1. Switch check & Tank pressure stabilization
To perform NVLD Leak Test Diagnosis, ECM software skips the normal process and starts diagnosis directly after Leak Test Diagnosis requests. When Leak Test Diagnosis is requested by external tool, ECM requests HCU to stop engine. When the engine stops, ECM fully opens PCSV to check NVLD pressure switch stuck failure and to stabilize tank pressure before starting Leak Test Diagnosis. If any switch stuck failure is detected, Leak Test Diagnosis ends and reports the results via tool.
2. Small & Large leak diagnosis
After checking switch stuck and pressure stabilization, ECM requests HCU to run engine and the target idle is 1500rpm for running stability. ECM opens PSCV and checks NVLD pressure switch position until the switch is closed. The longer switch closed time is, the bigger leak size can be estimated. ECM converts the switch closed time into leakage size and reports the results. If no leakage or small leak is detected, Leak Test Diagnosis ends. But if large leakage failure is detected, the process goes to the next step.
3. PCSV plausibility diagnosis
When any large leak failure is detected at previous status, ECM performs PCSV stuck diagnosis to check the root cause to make large leak. ECM opens PCSV and checks the diagnosis results. If the diagnosis results are acceptable, ECM finishes Leak Test Diagnosis and confirms large leakage failure. But if the results are out of range, ECM tries PCSV plausibility diagnosis max 3 times. When the results are still unsatisfactory even after 3 trials. ECM confirms PCSV stuck failure and reports the results.
4. Leak Test Diagnosis cancelling
If any conditions are not satisfied, ECM stops the process and reports the cancel reason via scan tool. An engineer can check the root cause and solve the problems to cause stop the process.
Evaporative And ORVR Emission Control System
This system consists of a fill vent valve, fuel shut-off valve, fuel cut valve (for roll over), two way valve (pressure/vacuum relief), fuel liquid/vapor separator which is installed beside the filler pipe, charcoal canister which is mounted under the rear floor LH side member and protector, tubes and miscellaneous connections.
While refueling, ambient air is drawn into the filler pipe so as not to emit fuel vapors in the air. The fuel vapor in the tank is then forced to flow into the canister via the fill vent valve. The fuel liquid/vapor separator isolates liquid fuel and passes the pure vapor to the charcoal canister.
While the engine is operating, the trapped vapor in the canister is drawn into the intake manifold and then into the engine combustion chamber. Using this purge process, the charcoal canister is purged and recovers its absorbing capability.
