Diagnostic Method

Perform the diagnosis under the conditions, and return the tank pressure to atmosphere.

Tank pressure > 0.9 kPa (67.5 mmHg, 2.7 inHg) after 0.1 seconds:

Cancel the leak check. (Change to Mode A, Tank pressure > 0.9 kPa (67.5 mmHg, 2.7 inHg).)

DTC P0457

DTC P1443

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. Under this condition, the valve cannot be opened for the pressure control solenoid valve structure if the negative pressure is larger than electromagnetic force when pressure control solenoid valve solenoid is set to ON in order to open the valve.

Fig 1: Identifying Pressure Control Solenoid Valve Close

Courtesy of SUBARU OF AMERICA, INC.

Fig 2: Identifying Solenoid Valve

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

Fig 3: CCV Closed Fixation Diagnosis Circuit Diagram

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Fig 4: Normal Operation Graph

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• evptez - evptezha =< 0.4 kPa (3.0 mmHg, 0.12 inHg)
• evptezini - evptezha =< 1.0 kPa (7.5 mmHg, 0.295 inHg)

  Judge normal when these calculations are completed.

Fig 5: Drain Valve Close Fixation Graph

Courtesy of SUBARU OF AMERICA, INC.

• evptezini - evptezha > 0.6 kPa (4.5 mmHg, 0.177 inHg)
• evptezini > 1.0 kPa (7.5 mmHg, 0.295 inHg)

  Judge normal when these calculations are completed.

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 below are completed in 3 seconds after Mode Z started.

Fig 6: Threshold Value Table (1 Of 3)

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Abnormality Judgment 

If OK judgment cannot be made, extend Mode Z 16 seconds more, and judge NG when all the criteria below the completed in 16 seconds.

Fig 7: Threshold Value Table (2 Of 3)

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1. Time Needed for Diagnosis:  16 seconds
2. Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cycles.

Finish the evaporative emission control system diagnosis when making NG judgment for drain valve close fixation.

Cancel the evaporative emission control system diagnosis when the OK/NG judgment for drain valve close fixation and purge control solenoid valve open fixation cannot be made in Mode Z.

DTC P0442

DTC P0456

DTC P0457

• 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: 

Calculate the tank pressure variation amount (P1) in Mode A. After calculating P1, change to Mode B.

Mode B: 

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 below is completed.

Finish the Evap. diagnosis when judging large leak (35 seconds) in 0.04-inch diagnosis. Cancel the diagnosis (62 seconds) in 0.02-inch diagnosis.

Abnormality Judgment 

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

Specified Time

High vehicle speed mode (Vehicle speed >= 72 km/h (45 MPH)); 35 seconds

Low vehicle speed mode (Vehicle speed < 72 km/h (45 MPH)); 18 seconds

Fig 8: Threshold Value Table (3 Of 3)

Courtesy of SUBARU OF AMERICA, INC.

Cancel the diagnosis when the NG judgment does not completed in the specified time.

Mode C: 

Stop the introduction of negative pressure. (Wait until the tank pressure returns to the start level of P2 calculation.)

Change to Mode D when the tank pressure returns to the start level of P2 calculation.

Judge immediate OK and change to Mode E when it does not return in spite of spending the specified time.

Fig 9: Judge Immediate OK Table

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Mode D: 

Monitor the pressure variation in the tank 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.

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

Abnormality Judgment 

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

Abnormality Judgment 

Judge NG when the criteria below are completed.

Fig 13: Fuel Pressure Table

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Normality Judgment 

Judge OK when the criteria below are completed.

Fig 15: Fuel Pressure Table

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If not judged OK or NG, repeat the diagnosis.

Fig 16: Judged Ok Diagram

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Fig 17: Judged NG Diagram

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Mode E: 

The tank pressure must become again as high as the atmospheric air pressure after the evaporation diagnosis. If the tank pressure does not become as high as the atmospheric air pressure, judge that CCV is blocked.

Fig 18: Threshold Value Table

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1. 0.04-inch: 30 - 70 seconds
2. 0.02-inch: 45 - 90 seconds

1. Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cycles.