P0456
DTC P0456 - EVAPORATIVE EMISSION CONTROL SYSTEM LEAK DETECTED (VERY SMALL LEAK)OUTLINE OF DIAGNOSIS
Perform the diagnosis of leakage of fuels system and valve functions.
In this system diagnosis, filter tank pressure is changed by setting ON/OFF each solenoid valve. And leakage and normality & abnormality of valve operation are judged by monitoring the pressure change status using the fuel tank pressure sensor. The diagnosis is performed in the order of Z (0.04-inch diagnosis only), Mode A, Mode B, Mode C, Mode D and Mode E.
0.04-inch Diagnosis
0.02-inch Diagnosis
Mode table for Evaporative Emission Control System diagnosis
COMPONENT DESCRIPTION
- Pressure Control Solenoid Valve
Pressure control solenoid valve maintains the fuel tank pressure equal to the atmospheric air pressure. Normally, the solenoid is set to OFF, and the valve mechanically opens and closes in accordance with the difference between the tank pressure and atmospheric air pressure, and the tank pressure and canister pressure. During the diagnosis, the valve is forcibly opened by setting the solenoid to ON.
- Valve Operation and Air Flow
As in the X parts, there are the area with atmospheric air pressure above the diaphragm and the area with tank pressure below the diaphragm. Also, as in the Y parts below, there are the area with tank pressure above the diaphragm and the area with canister pressure below the diaphragm. In the table below the air flow from each port in accordance with pressure difference is shown with the atmospheric air pressure port A, tank pressure port B and canister pressure port C.
When solenoid is ON
- CCV
CCV controls the ambient air to be introduced to the canister. Normally the solenoid is set to OFF and the valve is open. The valve is closed when the solenoid is set to ON only at the time of diagnosis.
- Tank Pressure Switching Solenoid
Purpose of this solenoid
Fuel tank pressure sensor detects the difference between the atmospheric air pressure and the tank pressure, and the ECM monitors the pressure difference.
Even if the tank pressure is constant, the atmospheric air pressure varies depending on the driving height, and the pressure signal transmitted to ECM will change.
Especially, in the small leakage [0.5 mm (0.02 inch)], minute change in the tank pressure has to be detected. This diagnosis period is long (approx. 29 seconds). And if the driving height changes during the diagnosis, the atmospheric air pressure changes. In this case, it becomes difficult to precisely detect the tank pressure variation, causing erroneous diagnosis. Therefore, using the atmospheric pressure switching solenoid, atmospheric air is sealed between the fuel tank pressure sensor and atmospheric pressure switching solenoid, maintaining the air pressure constant and enabling the detection of minute variation of tank pressure.
NOTE: ECM also has the atmospheric air pressure sensor, and always monitors atmospheric air. However, as the monitoring range is large, that is, 53.3 to 107 kPa (400 to 800 mmHg, 15.7 to 31.6 inHg), it is not suitable for detection of minute pressure variation.
In the case of small leakage diagnosis, the tank pressure variation is very small, that is, 0.13 to 0.26 kPa (1 to 2 mmHg, 0.04 to 0.08 inHg), and the fuel tank pressure sensor is equipped.
ENABLE CONDITION
GENERAL DRIVING CYCLE
0.04-inch Diagnosis
Perform the diagnosis only once in 856 seconds or more after starting the engine constantly at 32 km/h (19.9 MPH) or more.
Pay attention to the fuel temperature and fuel level.
0.02-inch Diagnosis
Perform the diagnosis in 335 seconds after starting the engine constantly at 68 km/h (42 MPH) or more, and perform OK/NG judgment.
If OK/NG judgment is not possible, repeat the diagnosis.
Pay attention to the fuel temperature and fuel level.
DIAGNOSTIC METHOD
- Diagnosing Function of Drain Valve and Purge Control Solenoid Valve
DTC
P0457 Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off)
P1443 Vent Control Solenoid Valve Function Problem
Purpose of Mode Z
When performing the leakage diagnosis of EVAP system, CCV and CPC have to operate normally. Therefore, mode Z is used to diagnose the CCV close fixation and CPC open fixation. If the CCV closed fixation trouble or CPC open fixation trouble is detected, the evaporation system leakage diagnosis is cancelled.
If the CCV closed fixation trouble occurred, negative pressure is generated from the engine to PCV when PCV is closed and CPC is opened. The occurrence of this status before the diagnosis results in erroneous diagnosis, because the valve cannot be opened for the PCV structure if the negative pressure is larger than electromagnetic force when PCV solenoid is set to ON in order to open the valve.
DIAGNOSTIC METHOD
CCV closed fixation diagnosis and CPC open fixation diagnosis are performed in mode Z as shown in the figure.
- Normal
- Purge control solenoid valve open fixation
- Drain valve close fixation
- Diagnosing Function of Drain Valve [P1443]
Perform the drain valve function (closed fixation) by closing the purge control solenoid valve and opening the purge control solenoid valve.
If the drain valve is normal, the canister pressure is always close to the atmospheric pressure because the drain valve is normally open. Thus, the tank pressure when closing the purge control solenoid valve and opening purge control solenoid valve becomes close to the atmospheric pressure. However, if a closed fixation failure is found in the drain valve, the canister pressure before the diagnosis is negative because the intake manifold negative pressure is introduced into the canister because the purge control solenoid valve is open. In this status, if the purge control solenoid valve is closed and purge control solenoid valve is opened, the tank pressure becomes negative because the canister negative pressure is introduced into the tank.
Perform the drain valve function diagnosis by monitoring the tank pressure variation when the purge control solenoid valve is closed and purge control solenoid valve is opened.
Normality Judgment
Judge OK when following malfunction criteria are completed within 3 seconds after starting Mode Z, and move to Mode A in case of OK.
Abnormality Judgment
If OK judgment is not possible, prolong Mode Z (16 seconds), and judge NG when all of malfunction criteria are completed with considering the following conditions in 16 seconds.
When the drain valve closed fixation NG judgment is performed, terminate the evaporation diagnosis.
Stuck Close of Drain Valve on Mode Z
If the stuck close of drain valve can not be judged OK/NG, cancel the EVAP. diagnosis.
- Diagnosing Function of Purge Control Solenoid Valve [P0457]
Perform the function diagnosis (open fixation) of the purge control solenoid valve by closing the drain valve with the purge control solenoid valve closed and purge control solenoid valve opened.
If the purge control solenoid valve is normal, the tank pressure does not change even if the drain valve is closed.
However, if a open fixation failure is found in the purge control solenoid valve, the tank pressure becomes negative because the intake manifold negative pressure is introduced into the tank when the drain valve is closed.
Perform the function diagnosis of the purge control solenoid valve by monitoring the tank pressure when the drain valve is closed.
Normality Judgment
Perform OK judgment in 3 seconds after starting Mode Z and move to Mode A if OK.
Diagnostic method and judgment value are the same as in case of purge control solenoid valve normal.
Abnormality Judgment
If OK judgment is not possible, prolong Mode Z (16 seconds), and judge NG when all of malfunction criteria are completed after 16 seconds considering the following conditions.
If the purge control solenoid valve open fixation NG judgment is performed, terminate the EVAP. diagnosis. If OK/NG judgment of the drain valve closed fixation and purge control solenoid valve open fixation is not possible in Mode Z, cancel the EVAP. diagnosis.
- Leakage Diagnosis
DTC
P0442 Evaporative Emission Control System Leak Detected (Small Leak)
P0456 Evaporative Emission Control System Leak Detected (Very Small Leak)
P0457 Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off)
DIAGNOSTIC METHOD
The diagnostic method consists of creating a sealed vacuum in the fuel tank and then determining the presence of leakage from the speed at which the tank internal pressure returns to atmospheric pressure.
Mode A; (Estimation of evaporation abundance)
The tank pressure increases in proportion to the evaporator generation because the purge control solenoid valve and drain valve are closed. P1 means the variation amount of this tank pressure. Move to Mode B after calculating P1.
Mode B; (Seal negative pressure)
Open the purge control solenoid valve, and introduce the negative pressure of the intake manifold into the tank.
Approx. 0 -> -1.4 kPa (0 -> -10.5 mmHg, O -> -0.41 inHg) (0.04-inch diagnosis)
Approx. 0 -> -3.05 kPa (0-> -22.875 mmHg, 0 -> -0.9 inHg) (0.02-inch diagnosis)
Move to Mode C when reaching the pressure above (target pressure).
Then, if the tank pressure does not become negative, judge that there is large leakage in the system. In 0.04-inch diagnosis, judge that there is large leakage (10 seconds or 25 seconds) and terminate the EVAP. diagnosis. In 0.02-inch diagnosis, cancel the diagnosis (20 seconds).
Abnormality Judgment
Judge NG (large leakage) when the malfunction criteria is completed.
Mode C; (Check increasing pressure)
Close the purge control solenoid valve and stop the introduction of negative pressure. (Wait until returning to P2 calculation start tank pressure)
When returning to P2 calculation start tank pressure, move to Mode D.
Judge premature OK and move to Mode E when not returning in the determined period of time.
Mode D; (Measurement of negative pressure variation)
Monitor the tank pressure variation with the purge control solenoid valve closed. In this case, the tank pressure increases (close to atmospheric pressure) because the evaporator is generated. However, if there is leakage, the pressure increases additionally. P2 means the variation amount of this tank pressure. After calculating P2, perform the small leakage diagnosis, and move to Mode E if normal. Terminate the EVAP. diagnosis if abnormal.
When Terminating Mode D
By assigning the variation values of tank pressure, P1 and P2, in the following formula, judge the system small leakage. If the calculated judgment value is larger than the threshold value, judge that there is a failure.
0.04-inch Diagnosis
Judge NG when the malfunction criteria is completed, and judge OK when the malfunction criteria is not completed.
0.02-inch Diagnosis
Abnormality Judgment
Judge NG when the malfunction criteria is completed, and judge OK when the malfunction criteria is not completed.
Abnormality Judgment
Judge NG and clear NG when the malfunction criteria is completed, and judge OK when the malfunction criteria is not completed.
If OK/NG judgment is not possible, repeat the diagnosis.
0.04-inch Diagnosis
- Drain Valve Property Diagnosis [P1443]
Mode E;
The tank pressure should return to the value equal to the atmospheric pressure because the status of the drain valve changes from closed to opened after the evaporation diagnosis is terminated (Mode C normal judgment or Mode D termination). If the value does not return, judge that the drain valve is closed. Judge NG when the following malfunction criteria is completed.
DTC CLEAR CONDITION
- When the OK idling cycle was completed 40 times in a row
- When "Clear Memory" was performed
MALFUNCTION INDICATOR LIGHT CLEAR CONDITION
- When the OK driving cycle was completed 3 times in a row
- When "Clear Memory" was performed
FAIL SAFE
Open the PCV when the drain valve malfunction occur.
ECM OPERATION AT DTC SETTING
- Memorize the freeze frame data. (For test mode $02)
- Memorize the diagnostic value and trouble standard value. (For test mode $06)