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, checking for leakage and valve function is conducted by changing the fuel tank pressure and monitoring the pressure change using the fuel tank pressure sensor. 0.04 inch diagnosis is performed in the order of mode Z, mode A, mode B, mode C, mode D and mode E, and 0.02 inch diagnosis is performed in the order of mode Y, 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

2. COMPONENT DESCRIPTION

- Pressure Control Solenoid Valve
PCV controls the fuel tank pressure to be equal to the atmospheric air pressure. Normally, the solenoid is set to OFF. And the valve opens and closes mechanically in accordance with the pressure difference between tank and atmospheric air, or tank and canister. The solenoid which is set to ON forces to open the valve.

- Valve Operation and Air Flow
In the above figure, divided by the diaphragm, the part above X is charged with atmospheric air pressure, and the part below X is charged with tank pressure. Also, the part above Y is charged with tank pressure, and the part below Y is charged with canister pressure. If the atmospheric air pressure port is A, tank pressure port is B, and canister pressure port is C, the air flows according to pressure difference from each port as shown in the table.

- When A < B (Solenoid OFF)

- When B < C (Solenoid OFF)

- When Solenoid is ON

- CCV
CCV controls the ambient air to be introduced to the canister.

- Tank Pressure Switching Solenoid
One of the atmospheric pressure switching solenoid 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 in)], 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 to 107 kPa (400 to 800 mmHg, 16 to 32 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 0.27 kPa (1 to 2 mmHg, 0.04 to 0.08 inHg) and the fuel tank pressure sensor is equipped.

3. ENABLE CONDITION

4. GENERAL DRIVING CYCLE
- 0.04-inch Diagnosis
- Perform the diagnosis only once in more than 856 seconds after the engine start at the constant driving speed of 32 km/h (20 MPH) or more.
- Pay attention to the fuel temperature and fuel level.
- 0.02-inch Diagnosis
- Perform diagnosis in more than 335 seconds after engine start at the constant speed of 68 km/h (42 MPH) or more, and then terminate the diagnosis when judged OK or NG.
- If not judged OK or NG, repeat the diagnosis until judged OK or NG.
- Pay attention to the fuel temperature and fuel level.

5. DIAGNOSTIC METHOD
- MODE Z (Purge control solenoid valve open malfunction diagnosis, CPC close malfunction diagnosis)
DTC P0457
DTC P1443

- 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 EVAP system leakage diagnosis is cancelled.

If the CCV closed fixation trouble occurred, negative pressure is generated from the engine to pressure control solenoid valve when pressure control solenoid valve is closed and CPC is opened. In this status, the pressure control solenoid valve solenoid, which is set to ON, does not open the valve for its structure when the negative pressure is larger than electromagnetic force.

- Diagnostic method
CCV closed fixation diagnosis and CPC open fixation diagnosis are performed in mode Z as shown in the figure.

- Normal Operation

- Purge Control Solenoid Valve Open Fixation

- Drain Valve close fixation

- Diagnosing Function of CCV [P1443]
CCV functional diagnosis is performed by monitoring the tank pressure variation in Mode Z.

Normality Judgment
Judge OK and change to Mode A when the criteria are completed in 3 seconds after Mode Z started.

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 drain valve close fixation and purge control solenoid valve open fixation cannot be made in Mode Z.

- Leak Diagnosis
DTC P0442
DTC P0456
DTC P0457

- 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 gas yield)
Calculate the tank pressure variation amount (P1). After calculating P1, change to Mode B.

Mode B; (Seal negative pressure)
Introduce the negative pressure in the intake manifold to the tank.
Approx. 0 -> -1.4 kPa (0 -> -10.5 mmHg, 0 -> -0.41 inHg) (0.04-in diagnosis)
Approx. 0 -> -3.05 kPa (0 -> -22.9 mmHg, 0 -> -0.9 inHg) (0.02-in diagnosis)

When the pressure above (desired negative pressure) is reached, Mode C is entered. In this case, if the tank pressure does not become the desired negative pressure, judge that there is a large leakage in the system.

Judge NG when the malfunction criteria is completed. Finish the Evap. diagnosis when judging large leak (10 seconds or 25 seconds) in 0.04-inch diagnosis. Cancel the diagnosis (10 to 20 seconds) in 0.02-inch diagnosis.

Abnormality Judgment
Judge NG (large leak) when the criteria are completed in the specified time.

Mode C; (Check increasing pressure)
Stop the introduction of negative pressure. (Wait until returning target pressure.) When returning to target pressure, move to Mode D. Judge immediate OK and change to Mode E when it does not return in spite of spending the specified time.

Mode D; (Measurement of negative pressure changes)
Monitor the tank pressure variation in Mode D. In this case, the tank pressure increases, that is, the pressure becomes as high as the atmospheric air pressure, because evaporator is generated. However, if any leakage exists, the pressure increases additionally in proportion to this leakage. The pressure variation of this tank is P2.

After calculating P2, perform small leak diagnosis and change to Mode E if normal. Complete Evap. diagnosis if abnormal.

After Mode D
Assigning P1 and P2, which are tank variations measured in Mode A and Mode B, to the formula, judge the small leakage of the system. If the measured judgment value exceeds the threshold value, it is judged to be malfunction.

0.04-inch Diagnosis

Abnormality Judgment
Judge NG when the criteria are completed and judge OK when not completed.

0.02-inch Diagnosis

Abnormality Judgment
Judge NG when the criteria are completed.

Normality Judgment
Judge OK when the criteria are completed.

If not judged OK or NG, repeat the diagnosis until judged OK or NG.

- CCV Property Diagnosis [P1443]

Mode E;
The tank pressure must become again as high as the atmospheric air pressure after the evaporation diagnosis (normal judgment on Mode C or after Mode D). If the tank pressure does not become as high as the atmospheric air pressure, judge that CCV is blocked. Judge NG when the criteria are completed.

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
Atmospheric purge solenoid function malfunction; Open the pressure control solenoid valve.

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)