EVAP Leak Check System Description
EVAP Leak Check System DescriptionThe ECM executes "Large Leak, Small Leak and Stuck Open/Close" and "Very Small Leak Test" in order to determine if the EVAP system is leaking or stuck open/close.
Large Leak, Small Leak and Stuck Open/Close Test
This test is for detecting the large leaking, the small leaking and the stuck open/close in the EVAP system as follows.
Phase A: Stuck Close of EVAP Canister Vent Solenoid Valve Test
If the EVAP vent system is restricted, a leakage of EVAP system will NOT be properly detected. The ECM tests this by commanding the EVAP canister purge valve ON, open; and commanding the EVAP canister vent solenoid valve OFF, open; and monitoring the fuel tank pressure for an increase in vacuum. If ECM detects that the vacuum increases more than a specified value on 2 consecutive tests, "DTC P2422: Evaporative Emission System Vent Valve Stuck Closed" sets.
Phase B: Stuck Open of EVAP Canister Purge Valve Test
If the EVAP canister purge valve does not seal properly, a leakage of EVAP system will NOT be properly detected. The ECM tests for this by commanding the EVAP canister purge valve OFF, closed; and EVAP canister vent solenoid valve ON, closed; sealing the system, and monitoring the fuel tank pressure for an increase in vacuum.
If the ECM detects that the vacuum increases more than a specified value on 2 consecutive tests, "DTC P0441: Evaporative Emission System Incorrect Purge Flow" sets.
Phase C: Stuck Close of EVAP Canister Purge Valve Test and Large Leak Test
The ECM will command the EVAP canister vent solenoid valve ON, closed, and command the EVAP purge valve ON, open, with the engine running, allowing engine vacuum into the EVAP system.
The ECM monitors the fuel tank pressure to verify that the system is able to reach a predetermined level of vacuum within a set amount of time.
If the ECM detects that the vacuum increases more than a specified value quickly on 2 consecutive tests, "DTC P0441: Evaporative Emission System Incorrect Purge Flow" sets. If the ECM does NOT detect that the specified vacuum value is achieved on 2 consecutive tests, "DTC P0455: Evaporative Emission System Leak Detected (Large Leak)" sets.
Phase D: Small Leak Test
The ECM then commands the EVAP canister purge valve OFF, closed, sealing the system and monitors the vacuum value for decay.
For other than Mexican specification, the vacuum decay value is utilized a trigger for the very small leak test.
For Mexican specification, If the ECM detects that the vacuum decay value is more than a specified value on 2 consecutive tests, "DTC P0442: Evaporative Emission System Leak Detected (Small Leak)" sets.
NOTE: "DTC P0442: Evaporative Emission System Leak Detected (Small Leak)" is only detected in the vehicle for Mexican specification.
Very Small Leak Test
NOTE: "Very small leak test" is only executed for the vehicle other than Mexican specification.
The engine off natural vacuum diagnostic is the very small leak test for the EVAP system. The engine off natural vacuum diagnosis monitors the EVAP system pressure or vacuum after the ignition switch OFF when the monitoring conditions are met.
The engine off natural vacuum diagnosis utilizes the temperature changes and the resulting naturally occurring vacuum or pressure in the fuel tank immediately following a drive cycle. When the vehicle is driven, the temperature in the fuel tank rises. When the vehicle is parked with the engine OFF and ignition switch OFF, the temperature in the fuel tank will continue to rise for a period of time, and then begin to decrease. The engine off natural vacuum diagnosis relies on this temperature change, and the corresponding pressure change to determine if the EVAP system leak is present.
The engine off natural vacuum diagnosis is designed to detect leaks as small as 0.5 mm (0.020 in). The diagnosis can determine if a very small leak is present based on vacuum or pressure readings in the EVAP system.
When a 0.5 mm (0.020 in) leak is present, almost no pressure or vacuum is measured. If the average of measured pressure from the last 6 measurements is higher than a specified value, "DTC P0456: Evaporative Emission System Leak Detected (Very Small Leak)" sets.
Monitoring Condition
Each test executes when all the following conditions met.
Large leak, small leak and stuck open/close test:
- Engine: Idling condition
- vehicle'speed < specified value
- Fuel control: Close loop
- ECT at engine start: within specified range (cold start)
- ECT at engine start - ambient temperature at engine start < specified value
- Ambient temperature: within specified range
- Time after engine start > specified time or fuel system adaptation stable
- Fuel level: within specified range
- BARO > specified value
- Battery voltage: within specified range
Very Small Leak Test:
- Ignition switch: OFF
- Vacuum decay gradient in "Large Leak, Small Leak and Stuck Open/Close Test" > specified value or "Large Leak, Small Leak and Stuck Open/Close Test : Incomplete before turning ignition switch OFF
- Driving distance before turning ignition switch OFF > specified value
- Engine run time before turning ignition switch OFF > specified value
- ECT < specified value
- ECT before turning ignition switch to OFF position > specified value
- ECT minus IAT < specified value
- Ambient temperature: within specified range
- Fuel level: within specified range
- BARO > specified value
- Battery voltage > specified value
- No refueling