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Home >> Subaru >> 2010 >> Legacy Premium, Standard >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 20 (Diagnostic Trouble Code (DTC) Detecting Criteria (H4DOTC)) >> Diagnostic Trouble Code (DTC) Detecting Criteria >> DTC P0442 Evaporative Emission Control System Leak Detected (Small Leak) >> Outline Of Diagnosis

Outline Of Diagnosis

WARNING: This page is about a different variant/trim than selected.

Check if there is a leakage in fuel system or not, and perform the function diagnosis of valve.

Fig 1: Evaporative Emission Control System Diagram
G06647921Courtesy of SUBARU OF AMERICA, INC.

In this system diagnosis, check for leakage and valve function is conducted by changing the fuel tank pressure and monitoring the pressure change using the fuel tank pressure sensor. When in 0.04 inch diagnosis, perform in the order of mode Z → mode A → mode B → mode C and mode D; When in 0.02 inch diagnosis, perform in the order of mode A → mode B → mode C → mode D and mode E.

0.04-inch Diagnosis 

Fig 2: Large Leakage Judgement Communication Chart
G05661537Courtesy of SUBARU OF AMERICA, INC.
MODE DESCRIPTION CHART

Mode Mode Description Diagnosis Period
Mode Z (Purge control solenoid valve opening failure diagnosis) Perform purge control solenoid valve opening failure diagnosis from the size of tank pressure variation from diagnosis start. 0 ms + 3000 ms - 0 ms +3000 ms+ 13000 ms
Mode A (Estimated evaporation amount) Calculate the tank pressure change amount (P1). 10000 ms
Mode B (Sealed negative pressure, large leakage judgment) Decrease the pressure in the tank to the target value by introducing the intake manifold pressure to the fuel tank.
If the tank pressure cannot be reduced, it is diagnosed as large leak.
0 - 10000 ms + 25000 ms
Mode C (Pressure increase check, advanced OK judgment) Wait until the tank pressure returns to the target (start level of P2 calculation). If the tank pressure does not become the value, make advanced OK judgment. 0 - 23635 ms
Mode D (Negative pressure variation measurement, evaporation leakage diagnosis) Calculate the tank pressure variation (P2), and obtain the diagnostic value using P1 found in Mode A.
Perform the evaporation diagnosis using the diagnostic value.
0 ms + 10000 ms

Mode Table for Evaporative Emission Control System Diagnosis 

DIAGNOSTIC ITEM CHART

Mode Behavior of tank internal pressure under normal conditions Diagnostic item DTC
Mode Z Roughly the same as barometric pressure (Same as 0 kPa (0 mmHg, 0 inHg)) Purge control solenoid valve is judged to be open. P0457
Mode A Pressure is in proportion to amount of evaporative emission. - None
Mode B Negative pressure is formed due to intake manifold negative pressure Large leak P0457
Mode C Reaches target pressure - None
Mode D Pressure change is small. EVAP system large leak determination. [1.0 mm (0.04 in)] P0442

0.02-inch Diagnosis 

Fig 3: 0.02-Inch Diagnosis Mode Description Chart
G04998199Courtesy of SUBARU OF AMERICA, INC.
MODE DESCRIPTION CHART

Mode Mode Description Diagnosis Period
Mode A (0 point compensation) When the pressure in the tank is not near 0 mmHg, wait until it returns to 0 point (near 0 mmHg). 0 - Value of Map 1
Mode B (Negative pressure introduced) Decrease the pressure in the tank to the target value by introducing the intake manifold pressure to the fuel tank. 0 - Value of Map 2
Mode C (Negative pressure maintained) Wait until the tank pressure returns to the target (start level of P2 calculation). Value from Map 3
Mode D (Negative pressure change calculated) Calculate the time it takes for the tank pressure to change to the Mode E shifting pressure. If the tank pressure does not change to the Mode E shifting pressure, make advanced OK judgment. 0 - 0 ms + Value from Map 4
Mode E (Evaporation generated amount calculation) Calculate the amount of evaporation (P1). 0 - 0 ms + Value from Map 4 + Value from Map 5

Map 1 

FUEL LEVEL REFERENCE

Fuel level ( , US gal, lmp gal) 10 27, 7.13, 5.94 43, 11.36, 9.46 59.5, 15.72, 13.09
Time Needed for Diagnosis (ms) 9216 9216 7936 4736

Map 2 

FUEL LEVEL REFERENCE

Fuel level ( , US gal, lmp gal) 10 27, 7.13, 5.94 43, 11.36, 9.46 59.5, 15.72, 13.09
Time Needed for Diagnosis (ms) 21180 23924 24931 24931

Map 3 

FUEL LEVEL REFERENCE

Fuel level ( , US gal, lmp gal) 10 27, 7.13, 5.94 43, 11.36, 9.46 59.5, 15.72, 13.09
Time Needed for Diagnosis (ms) 51830 32722 18045 13071

Map 4 

FUEL LEVEL REFERENCE

Fuel level ( , US gal, lmp gal) 10 20, 5.28, 4.4 30, 7.93, 6.6 40, 10.57, 8.8 50, 13.21, 11 60, 15.85, 13.2
Time Needed for Diagnosis (ms) 200000 200000 200000 200000 200000 200000

Map 5 

FUEL LEVEL REFERENCE

Fuel level ( , US gal, lmp gal) 10 20, 5.28, 4.4 30, 7.93, 6.6 40, 10.57, 8.8 50, 13.21, 11 60, 15.85, 13.2
Time Needed for Diagnosis (ms) 80000 70000 60000 60000 60000 60000