Key-off monitor
This monitoring system checks for canister pump module malfunctions and leaks from the EVAP and closed tank systems. Be sure to leave the vehicle for at least 5 hours to sufficiently cool the fuel and stabilize fuel tank pressure. This makes EVAP system monitoring more accurate.
HINT:
If the engine coolant temperature is 35°C (95°F) or more, 5 hours after the power switch has been turned OFF, the ECM will begin performing a monitor check after another 2 hours. If the engine coolant temperature is still 35°C (95°F) or more, 7 hours after the power switch has been turned OFF, the ECM will begin performing a monitor check after another 2.5 hours.
There are two methods for monitoring the EVAP system.
- If the fuel tank pressure is higher or lower than the atmospheric pressure, the system determines that there are no leaks in the closed tank system and the system will check for leaks from the piping and canister between the purge VSV and canister pump module. (Method A)
- If the fuel tank pressure is almost the same as the atmospheric pressure, vacuum pressure will enter the fuel tank and the system will check for leaks from the fuel tank after checking for leaks from the canister. (Method B)
CANISTER PRESSURE CHART
| Sequence | Operation | Description | Duration |
|---|---|---|---|
| - | ECM activation | Activated by soak timer, 5 hours (7 or 9.5 hours) after power switch turned OFF. | - |
| A | Atmospheric pressure measurement | Vent valve turned OFF (vent) and EVAP system pressure is measured by ECM in order to register atmospheric pressure. If pressure in EVAP system is not between 70 kPa and 110 kPa (525 mmHg and 825 mmHg), ECM cancels EVAP system monitor. | 10 seconds |
| B | First reference pressure measurement | In order to determine reference pressure standard, leak detection pump creates negative pressure (vacuum) through reference orifice and then ECM checks if leak detection pump and vent valve operate normally. | 60 seconds |
| C | EVAP system pressure measurement | Vent valve is turned ON (closed) to shut EVAP system. Negative pressure (vacuum) is created in EVAP system, and EVAP system pressure is then measured. Write down measured values as they will be used in leak check. If EVAP pressure does not stabilize within 15 minutes, ECM cancels EVAP system monitor. |
15 minutes |
| D | Purge VSV monitor | Purge VSV opens and then EVAP system pressure is measured by ECM. Large increase indicates normal. |
10 seconds |
| E | Second reference pressure measurement | After second reference pressure measurement, leak check is performed by comparing first and second reference pressure standards. If stabilized system pressure is higher than second reference pressure standard, ECM determines that EVAP system has a leakage. |
60 seconds |
| F | Fuel tank pressure is compared with atmospheric pressure. If thank pressure is higher than PH or lower than PL, ECM determines that EVAP system is normal and runs sequence I in method B. If tank pressure is around atmospheric pressure, ECM performs sequence G in method A. | 5 seconds | |
| G | Fuel tank pressure measurement | Vent valve is turned ON (closed). Fuel vapor-containment valve opens to allow negative pressure into the fuel tank and fuel tank pressure is measured. Write down measured values because they will be used in leak check. If fuel tank pressure does not stabilize within 15 minutes, ECM stops monitoring. |
15 minutes* |
| H | Third reference pressure measurement | After 3rd reference pressure measurement, leak check of fuel tank is performed. If recorded fuel tank pressure is higher than 3rd reference pressure, ECM determines that EVAP system has leakage. | 60 seconds |
| I | Fuel tank close valve close stuck check | Fuel vapor-containment valve is opened for a certain period of time to check whether the valve is stuck closed. | 0.1 second |
| J | Final check | Atmospheric pressure is measured and then monitoring result is recorded by ECM. | - |
| HINT: *: If there is only a small amount of fuel in the fuel tank, stabilizing the EVAP pressure takes longer than usual. |
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