P0457
DTC P0457 EVAPORATIVE EMISSION CONTROL SYSTEM LEAK DETECTED (FUEL CAP LOOSE/OFF)1. OUTLINE OF DIAGNOSIS
Perform the diagnosis of leakage of fuels system and valve functions.
In this system diagnosis, filter tank pressure is changed. 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 for 0.04-inch diagnosis in the order of Mode A, Mode B, Mode C and Mode D.
0.04-inch Diagnosis
0.02-inch Diagnosis
Mode table for Evaporative Emission Control System diagnosis
2. 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.
The solenoid which is set to ON forces to open the valve.
- Valve Operation and Air Flow
As in the X parts below, 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 A < B (Solenoid OFF)
When B < C (Solenoid OFF)
When solenoid is ON
- Drain valve
Drain valve controls the ambient air to be introduced to the canister.
- Tank Pressure Switching Solenoid
One of the fuel tank sensor control valve valves is connected to fuel tank pressure sensor and the other is released to atmosphere. The passage to fuel tank pressure sensor is usually released to atmosphere because the solenoid is set to OFF, but the solenoid which is set to ON closes the passage open to atmosphere.
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 fuel tank sensor control valve, atmospheric air is sealed between the fuel tank pressure sensor and fuel tank sensor control valve, 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.
3. ENABLE CONDITION
0.04-inch Diagnosis
0.02-inch Diagnosis
4. 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 (20 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.
5. DIAGNOSTIC METHOD
- Diagnosing Function of Drain Valve and Purge Control Solenoid Valve
DTC
P0457 Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off)
Purpose of Mode Z
When performing the leakage diagnosis of EVAP system, purge control solenoid valve have to operate normally. Therefore, mode Z is used to diagnose the purge control solenoid valve open fixation. If purge control solenoid valve open fixation trouble is detected, the evaporation system leakage diagnosis is cancelled.
Diagnostic method
Purge control solenoid valve open fixation diagnosis is performed in mode Z as shown in the figure.
- Diagnosing function of purge control solenoid valve [P0457]
Purge control solenoid valve functional diagnosis is performed by monitoring the tank pressure in Mode Z.
Normality Judgment
Judge OK when the criteria are satisfied in 3 seconds after Mode Z started, and change to Mode A.
- Normal
Abnormality Judgment
If OK judgment cannot be made, extend Mode Z 16 seconds more, and judge NG when all the criteria are completed in 16 seconds.
Finish the Evap. diagnosis when making NG judgment for purge control solenoid valve open fixation.
Cancel the Evap. diagnosis when the OK/NG judgment for purge control solenoid valve open fixation cannot be made in Mode Z.
- Purge control solenoid valve open fixation
- 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.
- The diagnosis is divided into the following five phases.
Mode A; (Estimation of evaporation abundance) Calculate the tank pressure variation amount (P1) at Mode A. Move to Mode B after calculating P1.
Mode B; (Seal negative pressure)
Introduce the negative pressure of the intake manifold into the tank.
Approx. 0 -> -1.4 kPa (0 -> -10.5 mmHg, 0 -> -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)
Stop the introduction of negative pressure. (Wait until returning to the start level of P2 calculation) When returning to the start level of P2 calculation, 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 in Mode D. 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.
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.
0.02-inch Diagnosis
Abnormality Judgment
Judge NG when the malfunction criteria is completed.
Normality Judgment
Judge OK when the malfunction criteria is not completed.
If OK/NG judgment is not possible, repeat the diagnosis.
6. DTC CLEAR CONDITION
- When the OK idling cycle was completed 40 times in a row
- When "Clear Memory" was performed
7. MALFUNCTION INDICATOR LIGHT CLEAR CONDITION
- When the OK driving cycle was completed 3 times in a row
- When "Clear Memory" was performed
8. FAIL SAFE
None
9. 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)